Although hydraulic fracturing in Liquid-Rich Unconventional Reservoirs (LUR) have become a norm, the recovery factor continues to be low. Use of Enhanced Oil Recovery (EOR) techniques in LUR have recently become more popular to improve the recovery. The objective of this study is to numerically investigate the advantages and disadvantages of the application of CO2 huff-n-puff technique in the LUR formations having complex fracture networks. The study explores the fluid flow mechanisms for oil recovery in the naturally fractured reservoir. A calibrated 3D mechanical earth model with geomechanical and petrophysical property from the Eagle Ford was used for the study. Complex hydraulic fracture model was used to simulate the hydraulic fractures, proppant and fluid distribution around the wellbore. Numerical reservoir simulation on a Perpendicular Bi-section (PEBI) grid was used to capture the permeability, porosity and conductivity distribution due to the proppants in the hydraulic fractures. CO2 huff-n-puff technique using numerical reservoir simulation is used to determine the well performance and recovery factor arising from reservoir fluid viscosity reduction and gas expansion. Effect of fluid thermodynamics to recovery systems in the low permeability reservoir medium is fully captured in approach. Equation of state prepared for simulating the CO2 impact on the oil is prepared with correlating the collected down hole oil sample. Numerical reservoir simulation study coupled with the complex fracture simulation model presents the insights of new means to improve RF in LUR through the injection of CO2. Such EOR method would be critical to increase the long term economic benefits. The study demonstrates that the infill well requirements can be mitigated if the EOR method of Huff-n-puff is utilized in cyclic modes over various time periods of production. Up to 9% extra RF was observed when CO2 Huff-n-puff technique was used as compared to production dependent only on hydraulic fracture stimulation. Parametric sensitivity on job sizes and start timing of EOR in a producing well is used to evaluate the RF. However, the hydraulic fracture geometry and the created footprint along with the time of injection has a larger effect in improving the EOR effectiveness. The methodology provides the demonstration of simulating the EOR methods in unconventional reservoirs for economic assessment. The workflow demonstrates modeling CO2 flooding as an EOR technique on the full wellbore level with complex hydraulic fracture geometry. The approach demonstrated here can be applied to other basins in the unconventional formations to improve the recovery factor.
In the past decade the industry has embraced unconventional resources; namely, shale oil and shale gas. After the initial drill-to-hold stage, multiwell pad drilling and stimulations are employed to exploit the acreage. Zipper fracturing is a technique that reduces the standby time (up to 50% reduction, when combined with the plug-and-perf isolation method). Because of this operational efficiency improvement, zipper fracturing has become one of the most common fracturing practices for unconventional reservoir stimulation. It has also been purported to increase production, which several authors have previously reported. There are also other studies showing no benefit of zipper fracturing on production performance.In this paper we have used a complex fracture network model, which we refer to as the Unconventional Fracture Model (UFM), to study zipper fracturing. The model simulates complex (branched) fracture propagation, associated stress shadows, fluid flow, and proppant transportation in the complex fracture network. The model solves the fully coupled problem of fluid flow in the fracture network and elastic deformation of the fracture. A key difference between UFM and the conventional planar fracture model is being able to simulate the interaction of hydraulic fractures with preexisting natural fractures (also referred as planes of weakness). The UFM simulates interwell and interstage stress shadows and honors both sequential fracturing and zipper fracturing scenarios' geomechanical interaction.In this paper, we present the results of a zipper and sequential fracturing study that includes the completion design optimization and the associated production performance in the Eagle Ford Shale. The study provides a workflow to optimize the completion and stimulation designs in pad development and to improve rate of return. The quantitative results show that zipper fracturing may not deliver a production benefit when compared with sequential fracturing and is a function of well spacing and perforation cluster spacing in a given area.
In today's data-driven economy, operators that integrate vast stores of fundamental reservoir and production data with the highperformance predictive analytics solutions can emerge as winners in the contest of maximizing estimated ultimate recovery (EUR). The scope of this study is to demonstrate a new workflow coupling earth sciences with data analytics to operationalize well completion optimization. The workflow aims to build a robust predictive model that allows users to perform sensitivity analysis on completion designs within a few hours. Current workflows for well completion and production optimization in unconventional reservoirs require extensive earth modeling, fracture simulation, and production simulations. With considerable effort and wide scale of sensitivity, studies could enable optimized well completion design parameters such as optimal cluster spacing, optimal proppant loading, optimal well spacing, etc. Yet, today, less than 5% of the wells fractured in North America are designed using advanced simulation due to the required level of data, skillset, and long computing times. Breaking these limitations through parallel fracture and reservoir simulations in the cloud and combining such simulation with data analytics and artificial intelligence algorithms helped in the development of a powerful solution that creates models for fast, yet effective, completion design. The approach was executed on Eagle Ford wells as a case study in 2016. Over 2000 data points were collected with completion sensitivity performed on a multithreaded cluster environment on these wells. Advanced machine learning and data mining algorithms of data analytics such as random forest, gradient boost, linear regression, etc. were applied on the data points to create a proxy model for the fracturing and numerical production simulator. With the gradient boost technique, over 90% accuracy was achieved between the proxy model and the actual results. Hence, the proxy model could predict the wellbore productivity accurately for any given change in completion design. The operators now had a much simpler model, which served as a plug-and-play tool for the completion engineers to evaluate the impact of changes in completion parameters on the future well performance and making fast-tracked economic decisions almost in real time. The approach can be replicated for varying geological and geomechanical properties as operations move from pad to pad. Although the need for heavy computing resource, simulation skillset, and long run times was eliminated with this new approach, regular QA/QC of the model through manual simulations makes the process more robust and reliable. The methodology provides an integrated approach to bridge the traditional reservoir understanding and simulation approach to the new big data approach to create proxies, which allows operators to make quicker decisions for completion optimization. The technique presented in this paper can be extended for other domains of wellsite operations such as well drilling, artificial lift, etc. and help operators evaluate the most economical scenario in close to real time.
Although hydraulic fracturing in liquid-rich unconventional reservoirs (LUR) has become a norm, the recovery factor continues to be low. Use of enhanced oil recovery (EOR) techniques in LUR has recently become more popular to improve the recovery. The objective of this study is to numerically investigate the advantages and disadvantages of the application of the CO2 huff-n-puff technique in LUR formations having complex fracture networks. The study explores the fluid flow mechanisms for oil recovery in a naturally fractured reservoir. A calibrated 3D mechanical earth model with geomechanical and petrophysical properties from the Eagle Ford was used for the study. A complex hydraulic fracture model was used to simulate the hydraulic fracture, proppant, and fluid distribution around the wellbore. Numerical reservoir simulation on perpendicular bisection (PEBI) grids was used to capture the permeability, porosity, and conductivity distribution due to the proppants in the hydraulic fractures. The CO2 huff-n-puff technique using numerical reservoir simulation was used to determine the well performance and recovery factor arising from reservoir fluid viscosity reduction and gas expansion. The effect of fluid thermodynamics to recovery systems in the low-permeability reservoir medium was fully captured in this approach. An equation of state prepared for simulating the CO2 impact on the oil was prepared with correlating the collected downhole oil sample. The numerical reservoir simulation study coupled with the complex fracture simulation model presents insights into a new means to improve the recovery factor (RF) in LUR through the injection of CO2. Such EOR method would be critical to increase the long-term economic benefits. The study demonstrates that that infill well requirements can be mitigated if the EOR method of huff-n-puff is utilized in cyclic modes over various time periods of production. Up to 9% extra RF was observed when the CO2 huff-n-puff technique was used as compared to production dependent only on hydraulic fracture stimulation. Parametric sensitivity on job sizes and start timing of EOR in a producing well was used to evaluate the RF. However, the hydraulic fracture geometry and the created footprint along with the time of injection have a larger effect in improving the EOR effectiveness. The methodology demonstrates the simulation of EOR methods in unconventional reservoirs for economic assessment. The workflow demonstrates modeling CO2 flooding as an EOR technique on the full wellbore level with complex hydraulic fracture geometry. The approach can be applied to unconventional formations in other basins to improve the recovery factor.
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