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Depletion effects occurs in unconventional reservoirs when the hydraulic fractured wells are completed within the drainage volume of existing producers. Field production and monitoring data show that the existing (parent) wells negatively affect the new (child) wells' productivity, making the new wells produce less than if all the wells are drilled and produced at the same time. This paper presents a systematic study on quantifying the offset well depletion effect in the Permian basin through advanced reservoir modeling and data analytics from field pilots.
The workflow starts with building an Earth model for parent wells in the area of interest, generating a hydraulic fracture network, and performing reservoir simulation for production forecast. The depletion effect, including changes in geomechanical properties on child wells, is properly updated in the Earth model and further captured through fracture geometry distortion and production decrease in the depleted environment. The results from the simulation models are further validated with actual field data. Simulations and pilot studies in both Midland and Delaware basins demonstrate that offset well depletion effect can have significant impact on production performance.
The ability to quantify depletion effect has significant business impacts on development sequence, facility design, completion design, and overall project economics. Analysis on various development scenarios was performed to evaluate the economic impact of depletion effect and determine how to mitigate this effect. Net present value (NPV) economic analysis of different simulation results indicates that time duration of production in the parent well ahead of child well has more impact on depletion effect than the distances between parent and child wells. As examples, depletion quantifications are applied to optimize well production near lease boundary with parent well depletion on the competitor land and guide section development strategy by evaluating pad sequence scenarios.
Abstract Inter-well communication in unconventional reservoirs has received huge attention due to its significant effects on well production. Though it has long been a known side effect of hydraulic fracturing, well interference has become more prominent and frequent as the industry moves to larger completion designs with closer well spacing and infill drilling. Fracturing of infill wells ("child" wells) directly places the older adjacent producing wells ("parent" wells) at risk of suffering premature change in production behavior. Some wells may never fully recover and, in worst cases, permanently stop producing after taking severe frac hits. This paper presents an automatic data-driven workflow developed to identify inter-well interference events and their impact on EUR (estimated ultimate recovery) based on changes in the well productivity trend. The innovative approach of the workflow is the ability to automatically analyze interference using the complete production history for all wells in a field, using routinely collected data and without introducing human bias in the derivation of the results, instead applying a consistent criteria. The final result is a comprehensive collection of all well interference events occurred in a field, which may be used as a training set for statistical and machine learning based models aiming at predicting such events. First, the automatic identification of anomalies in the well behavior was developed and criteria set to label the interference events. Next, probabilistic simulations are run to forecast multiple scenarios to quantify the impact of a well interference event reported in terms of change in cumulative oil production. Finally, every event is analyzed in the overall context of field operations, in an attempt to present possible causes which may explain the change of production behavior.
Abstract The present study provides a comprehensive set of new analytical expressions to help understand and quantify well interference due to competition for flow space between the hydraulic fractures of parent and child wells. Determination of the optimum fracture spacing is a key factor to improve the economic performance of unconventional oil and gas resources developed with multi-well pads. Analytical and numerical model results are combined in our study to identify, analyze, and visualize the streamline patterns near hydraulic fractures, using physical parameters that control the flow process, such as matrix permeability, hydraulic fracture dimensions and assuming infinite fracture conductivity. The algorithms provided can quantify the effect of changes in fracture spacing on the production performance of both parent and child wells. All results are based on benchmarked analytical methods which allow for fast computation, making use of Excel-based spreadsheets and Matlab-coded scripts. Such practical tools can support petroleum engineers in the planning of field development operations. The theory is presented with examples of its practical application using field data from parent and child wells in the Eagle Ford shale (Brazos County, East Texas). Based on our improved understanding of the mechanism and intensity of production interference, the fracture spacing (this study) and inter-well spacing (companion study) of multi-fractured horizontal laterals can be optimized to effectively stimulate the reservoir volume to increase the overall recovery factor and improve the economic performance of unconventional oil and gas properties.
Since late 2017, the Haynesville Shale has seen an uptick in activity as more operators have started to drill more new shale wells than at any other time since the industry was slowed due to declining oil price at the end of 2014. Some of the new activity has been focused on pushing the economic boundaries of the Haynesville shale out whereas others have focused on drilling infill wells or wells that are drilled between pre-existing wells (known as "parent wells"). Parent wells may cause pressure depletion in the reservoir, potentially hindering the performance of new infill wells. The distance from the parent well to an infill well along with the degree of reservoir depletion caused by the parent well impact, to varying degrees, the production results of the infill wells. It is important to design a completion program in the infill well that minimizes the potential negative impact of depletion. This paper presents detailed studies assessing the impact of the change in offset well spacing and reservoir depletion related to parent wells on infill well performance through modeling in the Haynesville shale. An actual reservoir dataset was utilized in the Haynesville shale to build the parent well hydraulic fracture and reservoir simulation models to account for fracture calibration and production history matching. The models' results were then used to evaluate the impact of production depletion on the stress reorientation and changes in stress magnitude through a coupled boundary element and finite element model residing in a geomechanics simulator. Three different production depletion times were modeled through the simulation, 0.5, 1, and 3 years, to understand the timing impact on the infill well production. After the stress in the model was updated for each case, a child well pad was added to the model adjacent to the parent well. The well spacing, stimulation job treatment, and fracture stimulation pump rates were all varied for child well simulation and evaluated to understand their impacts on the created complex fracture propagation and total system hydrocarbon recovery. In this study, more than 200 different scenarios were simulated by using cloud computation, and each parameter was compared for varying spacing scenarios for the three depletion time horizons. This study can help the understanding of well spacing, completion job design, and reservoir depletion impact on the new infill well performance and help the optimization of the infill well completion strategy to achieve optimum production performance for new infill wells and minimize communication or fracture hits to the existing parent wells in the Haynesville.
Xu, Tao (Schlumberger) | Lindsay, Garrett (Schlumberger) | Zheng, Wei (Schlumberger) | Yan, Qiyan (Schlumberger) | Escobar Patron, Katherine (Schlumberger) | Alimahomed, Farhan (Schlumberger) | Panjaitan, Maraden Luigie (Schlumberger) | Malpani, Raj (Schlumberger)
Abstract Since early 2016, commodity prices have been gradually increasing, and the Permian Basin has become the most active basin for unconventional horizontal well development. As the plays in the basin are developed, new infill wells are drilled near pre-existing wells (known as "parent wells"). The impact of pressure depletion caused by adjacent existing producers may have a larger role in the performance of these new infill wells. How the various well spacing impact with the degree of reservoir pressure depletion from parent well is more important than ever for operators to optimize the completion design. Through data analytics and comprehensive fracture/reservoir modeling this paper studies how changes in well spacing and proppant volume in the Spraberry, a main formation in the Permian Basin, will impact new infill well performance. The studies in this paper are focused on the Midland Basin. A public database was used to identify the number of parent and child wells in the Midland basin. Data analysis of production normalized by total proppant and lateral length shows that parent wells outperform infill, or child, wells. To further understand the relationship between parent and child wells, a reservoir dataset for the Spraberry formation was used to build a hydraulic fracture and reservoir simulation model for both the parent well and a two-well infill pad. After production history matching a P50 type well as the parent well, three periods of production depletion were modeled (6 months, 3 years and 5 years) to understand the timing impact on the infill well production. A geomechanical finite-element model (FEM) was then used to quantify the changes to the magnitude and azimuth of the in-situ stresses from the various reservoir depletion scenarios. A two-well infill pad was then simulated into the altered stress field next to the parent well at various spacings between the parent and child wells. A sensitivity was then performed with different stimulation job sizes to understand the volume impact on created complex fracture propagation and total system recovery. This study can help operators understand how well spacing, reservoir depletion, and completion job size impact the infill well performance so they can optimize their infill well completion strategy.
Abstract Parent-child relationship is becoming a topic of high interest in the Permian Basin as more infill wells are being drilled at various times after the parent well has been produced. This paper uses an advanced modelling workflow to determine the impact of parent depletion on infill well spacing at various periods of the parent well production. As the parent well is being produced, constant well spacing based on virgin condition becomes problematic because pressure depletion around the well leads to change in stress magnitude and orientations. This change in reservoir conditions, is critical for planning infill well. Parent well depletion results in potential negative impact including: –Asymmetric fracture propagation from the child well into the depleted area around the parent well –Potential detrimental fracturing hits to the parent well These effects would potentially impair the production performance of both parent and infill wells, further reducing the overall pad efficiency of the pad completions. Parent well behavior is simulated using an unconventional fracture model (UFM), and the model is calibrated with available treating data. The resulting hydraulic fracture uses an advanced unstructured gridding algorithm that accounts for a fine complex fracture network along the lateral. A high-resolution, numerical reservoir simulator that combines the unstructured grid, rock physics, and reservoir fluid data is then used to match historical production data. The reservoir pressure depletion profile at various timesteps (6, 12, 24, and 36 months) is used as an input to calculate the resulting stress field state via a finite element model. The resulting updated geomechanical properties are used to simulate the infill well hydraulic fracture geometries at various spacing; subsequent unstructured grids are created and used to forecast production. Results are then compared to quantify the impact of depletion. –Initial reservoir pressure and horizontal stress reduce progressively with increasing time of production of the parent well; the average minimum stress change in the stimulated area reaches 18% decrease after 36 months of parent production. –Hydraulic fractures of infill wells grow preferentially towards the adjacent depleted area, reducing fracture extension in virgin rock by more than 60%. –Parent well depletion impacts fracture geometry and production performance of child wells. –Wells closer to the parent are more affected with increasing depletion time; these wells see up to 50% in production reduction as compared to the parent well. –At larger well spacing, little impact is observed due to limited interference between wells. –To help mitigate the impact of parent depletion on infill wells, an innovative spacing scheme that consists of using varying spacing on infill wells closest to the depleted parent well can be used. For this study and with current reservoir properties and completion design, if the parent well has been produced for less than 12 months, infill wells should be placed a least 750 ft away from the parent and at least 900 ft away for parent production beyond 1 year.