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Manchanda, Ripudaman (The University of Texas at Austin) | Zheng, Shuang (The University of Texas at Austin) | Gala, Deepen (ExxonMobil Upstream Research Company) | Sharma, Mukul (The University of Texas at Austin)
Horizontal well fracturing is an established practice to improve the recovery of hydrocarbons from oil and gas reservoirs. To simulate fracture propagation, fracture closure during production and fracture reopening during fluid re-injection, it is essential to combine three important aspects of the problem: multiphase flow, geomechanics and fracture propagation. Current simulation software utilize separate models for these processes. Our objective in this paper is to present a streamlined workflow that we have developed to integrate these highly coupled processes into a single computationally efficient simulation model.
A fully coupled 3-D geomechanical reservoir simulator has been developed to perform multi-cluster hydraulic fracturing and reservoir simulations. The model (Multi-Frac-Res) uses coupled fluid and proppant transport in the fracture with multi-phase reservoir flow and reservoir stresses, in one system of equations. It also accurately models fluid and proppant distribution between multiple perforation clusters in the wellbore. Fracture closure during shut-in or production requires the use of implicit contact models and these models account for the impact of proppant embedment on fracture conductivity. The coupled system allows for seamless transition between fracture propagation, fracture closure, reservoir production and re-injection. This is done in one streamlined workflow without the need for inefficient transfer of information between different simulation software.
An effective hydraulic fracturing treatment aims at maximizing the EUR while maintaining high hydrocarbon production rates. The integrated model allows us to directly evaluate the impact of cluster spacing, frac fluid injection rate, proppant volume, and drawdown on the effectiveness of a hydraulic fracturing treatment. Simulation results are presented that show the relative importance of all the above parameters during the lifecycle of a typical horizontal well. We show how smaller cluster spacing can cause more interference between fractures and hamper the EUR. Larger proppant volume is shown to improve the conductivity of the created fractures and improve the productivity. Faster drawdown is shown to cause faster depletion and faster closure of the fracture but also helps in producing more fluid. Changes in the stress field around the fracture are presented and are shown to impact the growth of fractures in in-fill wells as well as the performance of refracturing treatments. These poroelastic effects are also shown to play a very important role in the growth and reorientation of fractures in injection wells during waterflooding.
Current simulation software utilize separate models for these processes leading to inefficient data transfer between several models that can cause loss of data. This study showcases an integrated model that can simulate the lifecycle of hydraulically fractured wells all the way from creation of the hydraulic fractures to production and reinjection and allows for a holistic comparison between scenarios by comparing productivity numbers and EUR estimates.
Frac-driven interactions (FDIs), more commonly known as frac hits, are becoming increasingly common as operators develop acreage near existing wells. These FDIs are commonly observed in an area of infill drilling in eastern Reagan County, Texas. To better understand their effects, a study was undertaken to document all FDIs observed during five years of field development in a fifteen-square-mile area. FDI frequency and intensity was found to be a function of (a) the parent well’s wellbore geometry, (b) offset direction between the parent and child well, (c) the presence or absence of a horizontal “buffer” well, and (d) distance between the parent and child wells. Horizontal parent wells received FDIs with greater frequency and intensity than vertical parent wells. Similarly, vertically stacked or directly offset parent wells received FDIs with greater frequency and intensity than indirectly offset or horizontally in-line parent wells. Horizontal parent wells commonly attenuate (or “buffer”) FDI frequency and intensity for other parent wells behind them (relative to the frac job). Distance between the parent and child well was found to have a strong negative correlation with FDI frequency and intensity but is more pronounced for vertical parent wells than horizontal parent wells. The majority of parent wells were found to receive either small FDIs or no FDI at all; thus, FDIs do not appear to pose a major risk to reserves within the study area contrary to many other unconventional plays. Although simple, the methodology was found to be a useful tool for understanding complex relationships between parent and child wells and may be applied to other development areas.
Recent industry analysis based on publicly available production data of most unconventional basins in the US have consistently highlighted the underperformance of child wells as compared to parent wells, although completion practices have continuously evolved. Industry publications have suggested that average productivity degradation of child wells can be up to 29% for some Delaware Basin operators. In some cases, the detrimental effects of parent-child relationships have also been observed on the parent wells after the stimulation of the child wells. In such an environment it is important to develop completion strategies to mitigate the negative effects of this parent-child relationship. In the Delaware Basin, the negative parent-child effect was successfully mitigated on two different zipper pads, with parent wells as close as 500 ft away from the zippered child wells. On the first pad, one parent well was completed and six months later two child wells were zippered with the closest child 1,000 ft away from the parent and pumped with far-field diversion. On the second pad, one parent well was completed and four months later three child wells were zippered with the closest child well 500 ft away from parent and far-field diversion pumped on the two closest child wells.
The stimulation treatment design was carefully designed to include far-field diverters on the stages near parent wells. Job size and far-field diverter quantity were determined using an integrated hydraulic fracture simulation software with an advanced particle transport model. Contingency scenarios were also prepared to facilitate real-time changes required when or if abnormal behavior was observed during the execution. The zipper sequence was also planned to help establish a stress-shadow effect near the parent well to further mitigate detrimental parent-child interactions. To monitor execution in real time and evaluate interactions between wells, high-frequency pressure gauges were installed on all observation wells including parent and child wells.
The completion design and far-field diversion treatment worked as planned for the first pad, with no significant well interference pressure signature observed on the monitoring well. For the second pad, the parent well saw pressure increases up to 700 psi during the treatment of a stage midway along the lateral of the closest child well which was completed with far-field diverter. Contingency plans were successfully executed, and no significant pressure increase was observed on the remainder of the lateral. Early production results indicate that the negative impacts of parent-child interactions were successfully mitigated on both pads, with the production of the parent wells quickly returned to their observed trends prior to child wells stimulation. Child wells production, when normalized both by lateral length and stimulation size, was on par with that of the parent well.
This session will discuss the impacts of well-to-well interference from a reserves and resource development standpoint. Economical aspects and legal considerations regarding parent-child interactions will be addressed. This session discusses the growing design considerations needed to effectively stimulate unconventional rock. We will discuss the workflows and information needed to execute an effective stimulation design in unconventional rock and set up the high level discussion around stimulation design. How does workflows effectively pass multi-disciplinary information to the completion design team, and how do the teams balance effective design, with well economics.
This ATW will be a follow-up to the highly successful 2019 event to bring some of the best and latest experience for Unconventional Well Completions and Stimulation practices and the relationship interdependence with resource development optimization and parent-child interactions. Sessions will frame the general technical considerations and trends and followed with Regional Sessions to highlight experiences and practices in the most active regional development areas. Understanding the interdependencies of the completions and stimulation projects with resource development optimization is critical to determine the best economic risk balance of resource development with managed over-capitalization. As unconventional developments mature, managing parent-child well interactions have become more challenging. This Applied Technology Workshop has been designed to share data, experiences, best practices and ideas from across North America Unconventional Resource Developments for Well Completions, Resource Development Optimization and Parent-Child Interaction.