From 3e49221d62736e3b16a85b2f68810f2a3150489a Mon Sep 17 00:00:00 2001
From: kbrunik <kbrunik@gmail.com>
Date: Wed, 14 Jan 2026 17:27:23 -0600
Subject: [PATCH 1/7] WIP arps decline curve

---
 examples/04_geo_h2/tech_config_natural.yaml   |   6 +
 .../hydrogen/geologic/simple_natural_geoh2.py | 125 ++++++++++++++++--
 .../geologic/test/test_geologic_h2.py         |   5 +
 3 files changed, 128 insertions(+), 8 deletions(-)

diff --git a/examples/04_geo_h2/tech_config_natural.yaml b/examples/04_geo_h2/tech_config_natural.yaml
index d23814653..3e84d4029 100644
--- a/examples/04_geo_h2/tech_config_natural.yaml
+++ b/examples/04_geo_h2/tech_config_natural.yaml
@@ -19,7 +19,13 @@ technologies:
         site_prospectivity: 0.7
         wellhead_h2_concentration: 95
         initial_wellhead_flow: 4000
+        gas_flow_density: 0.1
+        ramp_up_time_months: 6 #months
+        percent_increase_during_rampup: 0.05
         gas_reservoir_size: 1000000
+        use_arps_decline_curve: True
+        decline_fit_params:
+          fit_name: Eagle_Ford
       cost_parameters:
         use_cost_curve: True
         test_drill_cost: 500000
diff --git a/h2integrate/converters/hydrogen/geologic/simple_natural_geoh2.py b/h2integrate/converters/hydrogen/geologic/simple_natural_geoh2.py
index 0710244d2..c301fc85e 100644
--- a/h2integrate/converters/hydrogen/geologic/simple_natural_geoh2.py
+++ b/h2integrate/converters/hydrogen/geologic/simple_natural_geoh2.py
@@ -2,6 +2,7 @@
 from attrs import field, define
 
 from h2integrate.core.utilities import merge_shared_inputs
+from h2integrate.core.validators import range_val
 from h2integrate.converters.hydrogen.geologic.h2_well_subsurface_baseclass import (
     GeoH2SubsurfacePerformanceConfig,
     GeoH2SubsurfacePerformanceBaseClass,
@@ -32,15 +33,39 @@ class NaturalGeoH2PerformanceConfig(GeoH2SubsurfacePerformanceConfig):
             Hydrogen flow rate measured immediately after well completion, in kilograms
             per hour (kg/h).
 
+        gas_flow_density (float):
+            Density of the wellhead gas flow, in kilograms per cubic meter (kg/m^3).
+
+        ramp_up_time_months (float):
+            Number of months after initial flow from the well before full utilization.
+
+        percent_increase_during_rampup (float):
+            Percent increase in wellhead flow during ramp-up period in percent (%).
+
         gas_reservoir_size (float):
             Total amount of hydrogen stored in the geologic accumulation, in tonnes (t).
+
+        use_arps_decline_curve (bool):
+            Whether to use the Arps decline curve model for well production decline.
+
+        decline_fit_params (dict):
+            (Optional) Parameters for the Arps decline curve model, including:
+                - 'Di' (float): Decline rate.
+                - 'b' (float): Loss rate.
+                - 'fit_name' (str): Name of the well fit to use. If provided, overrides Di and b.
+                    Options are "Eagle_Ford" or "Permian" or "Bakken".
     """
 
     use_prospectivity: bool = field()
     site_prospectivity: float = field()
     wellhead_h2_concentration: float = field()
     initial_wellhead_flow: float = field()
+    gas_flow_density: float = field()
+    ramp_up_time_months: float = field()
+    percent_increase_during_rampup: float = field(validator=range_val(0, 100))
     gas_reservoir_size: float = field()
+    use_arps_decline_curve: bool = field()
+    decline_fit_params: dict = field(default=None)
 
 
 class NaturalGeoH2PerformanceModel(GeoH2SubsurfacePerformanceBaseClass):
@@ -109,7 +134,15 @@ def setup(self):
             "wellhead_h2_concentration", units="percent", val=self.config.wellhead_h2_concentration
         )
         self.add_input("initial_wellhead_flow", units="kg/h", val=self.config.initial_wellhead_flow)
+        self.add_input("gas_flow_density", units="kg/m**3", val=self.config.gas_flow_density)
         self.add_input("gas_reservoir_size", units="t", val=self.config.gas_reservoir_size)
+        self.add_input("ramp_up_time", units="yr/12", val=self.config.ramp_up_time_months)
+        self.add_input(
+            "percent_increase_during_rampup",
+            units="percent",
+            val=self.config.percent_increase_during_rampup,
+            desc="Percent increase in wellhead flow during ramp-up period in percent (%)",
+        )
 
         self.add_output("wellhead_h2_concentration_mass", units="percent")
         self.add_output("wellhead_h2_concentration_mol", units="percent")
@@ -118,6 +151,13 @@ def setup(self):
         self.add_output("max_wellhead_gas", units="kg/h")
 
     def compute(self, inputs, outputs):
+        n_timesteps = self.options["plant_config"]["plant"]["simulation"]["n_timesteps"]
+
+        # Coerce scalar inputs to Python scalars (handles 0-d and 1-d arrays)
+        ramp_up_time = float(np.asarray(inputs["ramp_up_time"]).item())
+        percent_increase = float(np.asarray(inputs["percent_increase_during_rampup"]).item())
+        init_wh_flow = float(np.asarray(inputs["initial_wellhead_flow"]).item())
+
         if self.config.rock_type == "peridotite":  # TODO: sub-models for different rock types
             # Calculate expected wellhead h2 concentration from prospectivity
             prospectivity = inputs["site_prospectivity"]
@@ -128,24 +168,93 @@ def compute(self, inputs, outputs):
 
         # Calculated average wellhead gas flow over well lifetime
         init_wh_flow = inputs["initial_wellhead_flow"]
-        lifetime = self.options["plant_config"]["plant"]["plant_life"]
-        n_timesteps = self.options["plant_config"]["plant"]["simulation"]["n_timesteps"]
-        avg_wh_flow = (-0.193 * np.log(lifetime) + 0.6871) * init_wh_flow  # temp. fit to Arps data
+
+        # Coerce scalar inputs to Python scalars (handles 0-d and 1-d arrays)
+        ramp_up_time = float(np.asarray(inputs["ramp_up_time"]).item())
+        percent_increase = float(np.asarray(inputs["percent_increase_during_rampup"]).item())
+        init_wh_flow = float(np.asarray(inputs["initial_wellhead_flow"]).item())
+
+        # Apply ramp-up assumed linear increase
+        ramp_up_steps = int(ramp_up_time * (n_timesteps / 12))  # hrs
+        if ramp_up_steps > 0:
+            ramp_up_flow = init_wh_flow * (1 + percent_increase / 100)
+            ramp_up_profile = np.linspace(init_wh_flow, ramp_up_flow, ramp_up_steps)
+        else:
+            ramp_up_flow = init_wh_flow
+        remaining_steps = (
+            n_timesteps * self.options["plant_config"]["plant"]["plant_life"] - ramp_up_steps
+        )  # remaining time steps in lifetime
+
+        # Use decline curve modeling if selected
+        if self.config.use_arps_decline_curve:
+            t = np.arange(remaining_steps)  # hrs
+            if self.config.decline_fit_params and "fit_name" in self.config.decline_fit_params:
+                # decline curves from literature is in million standard cubic feet per hour
+                ramp_up_flow_m3 = ramp_up_flow / inputs["gas_flow_density"]  # m3/h
+                # convert from m3/h to million standard cubic feet per hour (MMSCF/h)
+                ramp_up_flow_mmscf = ramp_up_flow_m3 / 28.3168 / 1e6
+
+                fit_name = self.config.decline_fit_params["fit_name"]
+                if fit_name == "Eagle_Ford":
+                    Di = 0.000157
+                    b = 0.932
+                elif fit_name == "Permian":
+                    Di = 0.000087
+                    b = 0.708
+                elif fit_name == "Bakken":
+                    Di = 0.000076
+                    b = 0.784
+                else:
+                    msg = f"Unknown fit_name '{fit_name}' \
+                        for Arps decline curve. Valid options are \
+                        'Eagle_Ford', 'Permian', or 'Bakken'."
+                    raise ValueError(msg)
+                decline_profile = self.arps_decline_curve_fit(t, ramp_up_flow_mmscf, Di, b)
+            else:
+                Di = self.config.decline_fit_params.get("Di")
+                b = self.config.decline_fit_params.get("b")
+                decline_profile = self.arps_decline_curve_fit(t, ramp_up_flow, Di, b)
+        else:
+            # linear decline for rest of lifetime
+            decline_profile = np.linspace(ramp_up_flow, 0, remaining_steps)
+
+        wh_flow_profile = np.concatenate((ramp_up_profile, decline_profile))
 
         # Calculated hydrogen flow out
         balance_mw = 23.32  # Note: this is based on Aspen models in aspen_surface_processing.py
         h2_mw = 2.016
         x_h2 = wh_h2_conc / 100
         w_h2 = x_h2 * h2_mw / (x_h2 * h2_mw + (1 - x_h2) * balance_mw)
-        avg_h2_flow = w_h2 * avg_wh_flow
+        avg_h2_flow = w_h2 * wh_flow_profile
 
         # Parse outputs
         outputs["wellhead_h2_concentration_mass"] = w_h2 * 100
         outputs["wellhead_h2_concentration_mol"] = wh_h2_conc
-        outputs["lifetime_wellhead_flow"] = avg_wh_flow
-        outputs["wellhead_gas_out_natural"] = np.full(n_timesteps, avg_wh_flow)
-        outputs["wellhead_gas_out"] = np.full(n_timesteps, avg_wh_flow)
-        outputs["hydrogen_out"] = np.full(n_timesteps, avg_h2_flow)
+        outputs["lifetime_wellhead_flow"] = np.average(wh_flow_profile)
+        # fill "wellhead_gas_out_natural" with first year profile from wh_flow_profile
+        outputs["wellhead_gas_out_natural"] = wh_flow_profile[:n_timesteps]
+        outputs["wellhead_gas_out"] = wh_flow_profile[:n_timesteps]
+        outputs["hydrogen_out"] = avg_h2_flow[:n_timesteps]
         outputs["max_wellhead_gas"] = init_wh_flow
         outputs["total_wellhead_gas_produced"] = np.sum(outputs["wellhead_gas_out"])
         outputs["total_hydrogen_produced"] = np.sum(outputs["hydrogen_out"])
+
+    def arps_decline_curve_fit(self, t, qi, Di, b):
+        """Arps decline model.
+
+        Relevant literature: https://doi.org/10.1016/j.jngse.2021.103818
+
+        Args:
+            t (np.array): Well production duration from max production.
+            qi (float): Maximum initial production rate.
+            Di (float): Decline rate.
+            b (float): Loss rate.
+
+        Returns:
+            (np.array): Production rate at time t.
+        """
+        qi = 0
+        if np.isclose(b, 0):
+            return qi * np.exp(-Di * t)
+        else:
+            return qi / (1 + b * Di * t) ** (1 / b)
diff --git a/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py b/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py
index 417d5c1ab..da2af3141 100644
--- a/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py
+++ b/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py
@@ -55,7 +55,12 @@ def geoh2_subsurface_well():
             "site_prospectivity": 0.7,
             "wellhead_h2_concentration": 95,
             "initial_wellhead_flow": 4000,
+            "gas_flow_density": 0.1,
+            "ramp_up_time": 6,
+            "percent_increase_during_rampup": 0.05,
             "gas_reservoir_size": 1000000,
+            "use_arps_decline_curve": True,
+            "decline_fit_params": {"fit_name": "Eagle_Ford"},
         },
     }
     tech_config_dict = {"model_inputs": subsurface_perf_config}

From fbee5ba6fcf285af48b005335d2916e1e9496cb3 Mon Sep 17 00:00:00 2001
From: kbrunik <kbrunik@gmail.com>
Date: Tue, 20 Jan 2026 11:32:24 -0600
Subject: [PATCH 2/7] update decline curve

---
 .../hydrogen/geologic/simple_natural_geoh2.py | 17 ++++++--
 .../geologic/test/test_geologic_h2.py         | 42 +++++++++++++++++++
 2 files changed, 56 insertions(+), 3 deletions(-)

diff --git a/h2integrate/converters/hydrogen/geologic/simple_natural_geoh2.py b/h2integrate/converters/hydrogen/geologic/simple_natural_geoh2.py
index c301fc85e..bf982a713 100644
--- a/h2integrate/converters/hydrogen/geologic/simple_natural_geoh2.py
+++ b/h2integrate/converters/hydrogen/geologic/simple_natural_geoh2.py
@@ -177,7 +177,7 @@ def compute(self, inputs, outputs):
         # Apply ramp-up assumed linear increase
         ramp_up_steps = int(ramp_up_time * (n_timesteps / 12))  # hrs
         if ramp_up_steps > 0:
-            ramp_up_flow = init_wh_flow * (1 + percent_increase / 100)
+            ramp_up_flow = init_wh_flow * (1 + percent_increase / 1)
             ramp_up_profile = np.linspace(init_wh_flow, ramp_up_flow, ramp_up_steps)
         else:
             ramp_up_flow = init_wh_flow
@@ -192,7 +192,7 @@ def compute(self, inputs, outputs):
                 # decline curves from literature is in million standard cubic feet per hour
                 ramp_up_flow_m3 = ramp_up_flow / inputs["gas_flow_density"]  # m3/h
                 # convert from m3/h to million standard cubic feet per hour (MMSCF/h)
-                ramp_up_flow_mmscf = ramp_up_flow_m3 / 28.3168 / 1e6
+                ramp_up_flow_mmscf = ramp_up_flow_m3 / 28316.846592  # 1 MMSCF = 28316.846592 m3
 
                 fit_name = self.config.decline_fit_params["fit_name"]
                 if fit_name == "Eagle_Ford":
@@ -210,6 +210,8 @@ def compute(self, inputs, outputs):
                         'Eagle_Ford', 'Permian', or 'Bakken'."
                     raise ValueError(msg)
                 decline_profile = self.arps_decline_curve_fit(t, ramp_up_flow_mmscf, Di, b)
+                # convert back to kg/h from MMSCF/h
+                decline_profile = decline_profile * 28316.846592 * inputs["gas_flow_density"]
             else:
                 Di = self.config.decline_fit_params.get("Di")
                 b = self.config.decline_fit_params.get("b")
@@ -219,6 +221,16 @@ def compute(self, inputs, outputs):
             decline_profile = np.linspace(ramp_up_flow, 0, remaining_steps)
 
         wh_flow_profile = np.concatenate((ramp_up_profile, decline_profile))
+        # plot the wellhead flow profile for debugging
+        import matplotlib.pyplot as plt
+
+        plt.plot(wh_flow_profile)
+        plt.xlabel("Time (hours)")
+        plt.ylabel("Wellhead Gas Flow (kg/h)")
+        plt.title("Wellhead Gas Flow Profile Over Well Lifetime")
+        plt.grid()
+        plt.show()
+        ##############
 
         # Calculated hydrogen flow out
         balance_mw = 23.32  # Note: this is based on Aspen models in aspen_surface_processing.py
@@ -253,7 +265,6 @@ def arps_decline_curve_fit(self, t, qi, Di, b):
         Returns:
             (np.array): Production rate at time t.
         """
-        qi = 0
         if np.isclose(b, 0):
             return qi * np.exp(-Di * t)
         else:
diff --git a/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py b/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py
index da2af3141..c3f941c66 100644
--- a/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py
+++ b/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py
@@ -96,6 +96,48 @@ def aspen_geoh2_config():
     return {"model_inputs": model_inputs}
 
 
+def test_natural_geoh2_well_performance(subtests, plant_config):
+    subsurface_perf_config = {
+        "shared_parameters": {
+            "borehole_depth": 300,
+            "well_diameter": "small",
+            "well_geometry": "vertical",
+        },
+        "performance_parameters": {
+            "rock_type": "peridotite",
+            "grain_size": 0.01,
+            "use_prospectivity": False,
+            "site_prospectivity": 0.7,
+            "wellhead_h2_concentration": 95,
+            "initial_wellhead_flow": 40000,
+            "gas_flow_density": 0.11741,
+            "ramp_up_time_months": 6,
+            "percent_increase_during_rampup": 0.05,
+            "gas_reservoir_size": 10000000,
+            "use_arps_decline_curve": True,
+            "decline_fit_params": {"fit_name": "Eagle_Ford"},
+        },
+    }
+    tech_config_dict = {"model_inputs": subsurface_perf_config}
+    subsurface_comp = NaturalGeoH2PerformanceModel(
+        plant_config=plant_config,
+        tech_config=tech_config_dict,
+        driver_config={},
+    )
+
+    prob = om.Problem()
+    prob.model.add_subsystem("perf", subsurface_comp, promotes=["*"])
+
+    prob.setup()
+    prob.run_model()
+
+    with subtests.test("Well hydrogen production"):
+        assert (
+            pytest.approx(np.mean(prob.model.get_val("perf.hydrogen_out", units="kg/h")), rel=1e-6)
+            == 603.4286677531819
+        ), 1e-6
+
+
 def test_aspen_geoh2_performance(subtests, plant_config, geoh2_subsurface_well, aspen_geoh2_config):
     prob = om.Problem()
     perf_comp = AspenGeoH2SurfacePerformanceModel(

From db2aa10a67387b269824f114387a59b180db0a67 Mon Sep 17 00:00:00 2001
From: kbrunik <kbrunik@gmail.com>
Date: Tue, 20 Jan 2026 14:26:29 -0600
Subject: [PATCH 3/7] update geoh2 and docstring

---
 examples/04_geo_h2/run_geo_h2.py              | 15 +++++++++++
 examples/04_geo_h2/tech_config_natural.yaml   |  2 +-
 .../hydrogen/geologic/simple_natural_geoh2.py | 26 +++++++++----------
 .../geologic/test/test_geologic_h2.py         |  8 +++---
 4 files changed, 32 insertions(+), 19 deletions(-)

diff --git a/examples/04_geo_h2/run_geo_h2.py b/examples/04_geo_h2/run_geo_h2.py
index 5b0938936..19215c6b4 100644
--- a/examples/04_geo_h2/run_geo_h2.py
+++ b/examples/04_geo_h2/run_geo_h2.py
@@ -8,6 +8,21 @@
 h2i_nat.run()
 h2i_nat.post_process()
 
+import matplotlib.pyplot as plt
+
+
+hydrogen_out = (
+    h2i_nat.prob.model.plant.geoh2_well_subsurface.simple_natural_geoh2_performance.get_val(
+        "hydrogen_out"
+    )
+)
+plt.plot(hydrogen_out)
+plt.xlabel("Time (hours)")
+plt.ylabel("Wellhead Gas Flow (kg/h)")
+plt.title("Wellhead Gas Flow Profile Over First Year")
+plt.grid()
+plt.show()
+
 
 # Create an H2I model for stimulated geologic hydrogen production
 h2i_stim = H2IntegrateModel("04_geo_h2_stimulated.yaml")
diff --git a/examples/04_geo_h2/tech_config_natural.yaml b/examples/04_geo_h2/tech_config_natural.yaml
index 3e84d4029..c4b090810 100644
--- a/examples/04_geo_h2/tech_config_natural.yaml
+++ b/examples/04_geo_h2/tech_config_natural.yaml
@@ -19,7 +19,7 @@ technologies:
         site_prospectivity: 0.7
         wellhead_h2_concentration: 95
         initial_wellhead_flow: 4000
-        gas_flow_density: 0.1
+        gas_flow_density: 0.11741 # for 95% h2
         ramp_up_time_months: 6 #months
         percent_increase_during_rampup: 0.05
         gas_reservoir_size: 1000000
diff --git a/h2integrate/converters/hydrogen/geologic/simple_natural_geoh2.py b/h2integrate/converters/hydrogen/geologic/simple_natural_geoh2.py
index bf982a713..2fd6aa69b 100644
--- a/h2integrate/converters/hydrogen/geologic/simple_natural_geoh2.py
+++ b/h2integrate/converters/hydrogen/geologic/simple_natural_geoh2.py
@@ -194,6 +194,7 @@ def compute(self, inputs, outputs):
                 # convert from m3/h to million standard cubic feet per hour (MMSCF/h)
                 ramp_up_flow_mmscf = ramp_up_flow_m3 / 28316.846592  # 1 MMSCF = 28316.846592 m3
 
+                # fits for MMSCF/h based on flow rates Figure 7 in Tang et al. (2024)
                 fit_name = self.config.decline_fit_params["fit_name"]
                 if fit_name == "Eagle_Ford":
                     Di = 0.000157
@@ -221,16 +222,6 @@ def compute(self, inputs, outputs):
             decline_profile = np.linspace(ramp_up_flow, 0, remaining_steps)
 
         wh_flow_profile = np.concatenate((ramp_up_profile, decline_profile))
-        # plot the wellhead flow profile for debugging
-        import matplotlib.pyplot as plt
-
-        plt.plot(wh_flow_profile)
-        plt.xlabel("Time (hours)")
-        plt.ylabel("Wellhead Gas Flow (kg/h)")
-        plt.title("Wellhead Gas Flow Profile Over Well Lifetime")
-        plt.grid()
-        plt.show()
-        ##############
 
         # Calculated hydrogen flow out
         balance_mw = 23.32  # Note: this is based on Aspen models in aspen_surface_processing.py
@@ -247,14 +238,21 @@ def compute(self, inputs, outputs):
         outputs["wellhead_gas_out_natural"] = wh_flow_profile[:n_timesteps]
         outputs["wellhead_gas_out"] = wh_flow_profile[:n_timesteps]
         outputs["hydrogen_out"] = avg_h2_flow[:n_timesteps]
-        outputs["max_wellhead_gas"] = init_wh_flow
+        outputs["max_wellhead_gas"] = ramp_up_flow
+        # this is lifetime flow which decreases over time
         outputs["total_wellhead_gas_produced"] = np.sum(outputs["wellhead_gas_out"])
         outputs["total_hydrogen_produced"] = np.sum(outputs["hydrogen_out"])
 
     def arps_decline_curve_fit(self, t, qi, Di, b):
-        """Arps decline model.
-
-        Relevant literature: https://doi.org/10.1016/j.jngse.2021.103818
+        """Arps decline curve model based on Arps (1945)
+            https://doi.org/10.2118/945228-G.
+
+        Other Relevant literature:
+            Tang et al. (2024) https://doi.org/10.1016/j.jngse.2021.103818
+            Adapted the Arps model from Table 2 to fit the
+            monthly gas rates from Figure 7 to characterize natural hydrogen
+            well production decline for the three oil shale wells
+            (Bakken, Eagle Ford and Permian).
 
         Args:
             t (np.array): Well production duration from max production.
diff --git a/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py b/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py
index c3f941c66..133a6588b 100644
--- a/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py
+++ b/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py
@@ -56,7 +56,7 @@ def geoh2_subsurface_well():
             "wellhead_h2_concentration": 95,
             "initial_wellhead_flow": 4000,
             "gas_flow_density": 0.1,
-            "ramp_up_time": 6,
+            "ramp_up_time_months": 6,
             "percent_increase_during_rampup": 0.05,
             "gas_reservoir_size": 1000000,
             "use_arps_decline_curve": True,
@@ -134,7 +134,7 @@ def test_natural_geoh2_well_performance(subtests, plant_config):
     with subtests.test("Well hydrogen production"):
         assert (
             pytest.approx(np.mean(prob.model.get_val("perf.hydrogen_out", units="kg/h")), rel=1e-6)
-            == 603.4286677531819
+            == 22649.432193239327
         ), 1e-6
 
 
@@ -161,7 +161,7 @@ def test_aspen_geoh2_performance(subtests, plant_config, geoh2_subsurface_well,
     with subtests.test("Well hydrogen production"):
         assert (
             pytest.approx(np.mean(prob.model.get_val("well.hydrogen_out", units="kg/h")), rel=1e-6)
-            == 603.4286677531819
+            == 2264.9432193239327
         ), 1e-6
 
 
@@ -246,7 +246,7 @@ def test_aspen_geoh2_refit_coeffs(
     with subtests.test("Well hydrogen production"):
         assert (
             pytest.approx(prob.model.get_val("well.hydrogen_out", units="kg/h"), rel=1e-6)
-            == 603.4286677531819
+            == 2264.9432193239327
         ), 1e-6
 
     with subtests.test("Refit Performance Coeff File"):

From 18c0dc9ed7fee7a7b75fb1f7ba95ac222c2e8297 Mon Sep 17 00:00:00 2001
From: kbrunik <kbrunik@gmail.com>
Date: Mon, 26 Jan 2026 15:26:34 -0600
Subject: [PATCH 4/7] update test

---
 .../converters/hydrogen/geologic/test/test_geologic_h2.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py b/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py
index 133a6588b..f702552d7 100644
--- a/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py
+++ b/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py
@@ -55,7 +55,7 @@ def geoh2_subsurface_well():
             "site_prospectivity": 0.7,
             "wellhead_h2_concentration": 95,
             "initial_wellhead_flow": 4000,
-            "gas_flow_density": 0.1,
+            "gas_flow_density": 0.11741,
             "ramp_up_time_months": 6,
             "percent_increase_during_rampup": 0.05,
             "gas_reservoir_size": 1000000,
@@ -168,9 +168,9 @@ def test_aspen_geoh2_performance(subtests, plant_config, geoh2_subsurface_well,
 def test_aspen_geoh2_performance_cost(
     subtests, plant_config, geoh2_subsurface_well, aspen_geoh2_config
 ):
-    expected_capex = 1795733.55
+    expected_capex = 4419318.42
     expected_opex = 4567464
-    expected_varopex = 984842.53
+    expected_varopex = 3613663.44
 
     prob = om.Problem()
     perf_comp = AspenGeoH2SurfacePerformanceModel(
@@ -245,7 +245,7 @@ def test_aspen_geoh2_refit_coeffs(
 
     with subtests.test("Well hydrogen production"):
         assert (
-            pytest.approx(prob.model.get_val("well.hydrogen_out", units="kg/h"), rel=1e-6)
+            pytest.approx(np.mean(prob.model.get_val("well.hydrogen_out", units="kg/h")), rel=1e-6)
             == 2264.9432193239327
         ), 1e-6
 

From a7573f4aa88a2e92c7058138585ae7cd758738ed Mon Sep 17 00:00:00 2001
From: kbrunik <kbrunik@gmail.com>
Date: Tue, 27 Jan 2026 09:52:24 -0600
Subject: [PATCH 5/7] update to be percent

---
 examples/04_geo_h2/tech_config_natural.yaml               | 2 +-
 examples/test/test_all_examples.py                        | 8 ++++----
 .../converters/hydrogen/geologic/simple_natural_geoh2.py  | 2 +-
 .../converters/hydrogen/geologic/test/test_geologic_h2.py | 4 ++--
 4 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/examples/04_geo_h2/tech_config_natural.yaml b/examples/04_geo_h2/tech_config_natural.yaml
index c4b090810..875931efc 100644
--- a/examples/04_geo_h2/tech_config_natural.yaml
+++ b/examples/04_geo_h2/tech_config_natural.yaml
@@ -21,7 +21,7 @@ technologies:
         initial_wellhead_flow: 4000
         gas_flow_density: 0.11741 # for 95% h2
         ramp_up_time_months: 6 #months
-        percent_increase_during_rampup: 0.05
+        percent_increase_during_rampup: 5 # percent
         gas_reservoir_size: 1000000
         use_arps_decline_curve: True
         decline_fit_params:
diff --git a/examples/test/test_all_examples.py b/examples/test/test_all_examples.py
index acb644faa..742944bec 100644
--- a/examples/test/test_all_examples.py
+++ b/examples/test/test_all_examples.py
@@ -1353,7 +1353,7 @@ def test_natural_geoh2(subtests):
                 np.mean(h2i_nat.model.get_val("geoh2_well_subsurface.hydrogen_out", units="kg/h")),
                 rel=1e-6,
             )
-            == 603.4286677531819
+            == 2264.943
         )
 
     with subtests.test("integrated LCOH"):
@@ -1361,7 +1361,7 @@ def test_natural_geoh2(subtests):
             pytest.approx(
                 h2i_nat.prob.get_val("finance_subgroup_h2.LCOH", units="USD/kg"), rel=1e-6
             )
-            == 1.59307314
+            == 0.6026907731
         )
     with subtests.test("subsurface Capex"):
         assert (
@@ -1385,14 +1385,14 @@ def test_natural_geoh2(subtests):
 
     with subtests.test("surface Capex"):
         assert (
-            pytest.approx(h2i_nat.model.get_val("geoh2_well_surface.CapEx"), rel=1e-6) == 1795733.55
+            pytest.approx(h2i_nat.model.get_val("geoh2_well_surface.CapEx"), rel=1e-6) == 4419318.42
         )
     with subtests.test("surface fixed Opex"):
         assert pytest.approx(h2i_nat.model.get_val("geoh2_well_surface.OpEx"), rel=1e-6) == 4567464
     with subtests.test("surface variable Opex"):
         assert (
             pytest.approx(h2i_nat.model.get_val("geoh2_well_surface.VarOpEx"), rel=1e-6)
-            == 984842.53
+            == 3613663.44
         )
     with subtests.test("surface adjusted opex"):
         surface_adjusted_opex = h2i_nat.prob.get_val(
diff --git a/h2integrate/converters/hydrogen/geologic/simple_natural_geoh2.py b/h2integrate/converters/hydrogen/geologic/simple_natural_geoh2.py
index 2fd6aa69b..ba97473dc 100644
--- a/h2integrate/converters/hydrogen/geologic/simple_natural_geoh2.py
+++ b/h2integrate/converters/hydrogen/geologic/simple_natural_geoh2.py
@@ -177,7 +177,7 @@ def compute(self, inputs, outputs):
         # Apply ramp-up assumed linear increase
         ramp_up_steps = int(ramp_up_time * (n_timesteps / 12))  # hrs
         if ramp_up_steps > 0:
-            ramp_up_flow = init_wh_flow * (1 + percent_increase / 1)
+            ramp_up_flow = init_wh_flow * ((100 + percent_increase) / 100)
             ramp_up_profile = np.linspace(init_wh_flow, ramp_up_flow, ramp_up_steps)
         else:
             ramp_up_flow = init_wh_flow
diff --git a/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py b/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py
index f702552d7..477599833 100644
--- a/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py
+++ b/h2integrate/converters/hydrogen/geologic/test/test_geologic_h2.py
@@ -57,7 +57,7 @@ def geoh2_subsurface_well():
             "initial_wellhead_flow": 4000,
             "gas_flow_density": 0.11741,
             "ramp_up_time_months": 6,
-            "percent_increase_during_rampup": 0.05,
+            "percent_increase_during_rampup": 5,
             "gas_reservoir_size": 1000000,
             "use_arps_decline_curve": True,
             "decline_fit_params": {"fit_name": "Eagle_Ford"},
@@ -112,7 +112,7 @@ def test_natural_geoh2_well_performance(subtests, plant_config):
             "initial_wellhead_flow": 40000,
             "gas_flow_density": 0.11741,
             "ramp_up_time_months": 6,
-            "percent_increase_during_rampup": 0.05,
+            "percent_increase_during_rampup": 5,
             "gas_reservoir_size": 10000000,
             "use_arps_decline_curve": True,
             "decline_fit_params": {"fit_name": "Eagle_Ford"},

From 02e5145849190f0516011623b528028eef5e6897 Mon Sep 17 00:00:00 2001
From: kbrunik <kbrunik@gmail.com>
Date: Tue, 27 Jan 2026 10:07:55 -0600
Subject: [PATCH 6/7] update documentation

---
 CHANGELOG.md                                | 1 +
 docs/technology_models/geologic_hydrogen.md | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b7f54bf5d..c20113d3e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@
 - Add geologic hydrogen surface processing converter
 - Add baseclass for caching functionality
 - Minor reorg for profast tools
+- Add Arps decline rate to natural geologic hydrogen model
 
 ## 0.5.1 [December 18, 2025]
 
diff --git a/docs/technology_models/geologic_hydrogen.md b/docs/technology_models/geologic_hydrogen.md
index c9f8ddd2d..99b52a847 100644
--- a/docs/technology_models/geologic_hydrogen.md
+++ b/docs/technology_models/geologic_hydrogen.md
@@ -24,6 +24,12 @@ The modeling approach in this performance model is informed by:
 - [Gelman et al. (USGS)](https://doi.org/10.3133/pp1900)
 - [Tang et al. (Southwest Petroleum University)](https://doi.org/10.1016/j.petsci.2024.07.029)
 
+The natural geologic hydrogen model is able to model well decline over time and there are two methods of decline.
+1. If not specified or `use_arps_decline_curve` is `False`: the decline rate will be linear over the lifetime of the well as defined in the attribute `plant_config["plant"]["plant_life"]`
+2. If `use_arps_decline_curve` is `True`: The well production will decline according to the Arps model as defined in [Tang et al. (Southwest Petroleum University)](https://doi.org/10.1016/j.petsci.2024.07.029). There are several options for using the decline curve to model well production.
+    1. `decline_fit_params` is a dictionary where a user can specify the decline rate and loss rate. It should be noted that typically the modeling of these decline rates are monthly. This model uses hourly timesteps so the decline and loss rate should be modified accordingly.
+    2. `decline_fit_params["fit_name"]` is an optional string that can be specified within the `decline_fit_params` dictionary that will model a decline rate similar to those noted at either the "Bakken", "Eagle Ford" or "Permian" shale wells documented in [Tang et al. (Southwest Petroleum University)](https://doi.org/10.1016/j.petsci.2024.07.029) Figure 7.
+
 (templeton-serpentinization-geoh2-performance)=
 ### Templeton Serpentinization GeoH2 Performance
 

From 9f4bdac92d0ba0274df70d9f61be8f42ff36a4b0 Mon Sep 17 00:00:00 2001
From: kbrunik <kbrunik@gmail.com>
Date: Tue, 27 Jan 2026 10:30:55 -0600
Subject: [PATCH 7/7] fix changelog

---
 CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 510a541f3..4ccf6b8ec 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -28,7 +28,7 @@
     listed at the bottom.
   - Remove unused dependencies.
   - Fixes typos for skipped folders.
-  - Add Arps decline rate to natural geologic hydrogen model
+- Add Arps decline rate to natural geologic hydrogen model
 
 ## 0.5.1 [December 18, 2025]