Impact of Well Spacing and Interference on Production Performance in Unconventional Reservoirs, Permian Basin
In the Permian basin, unconventional reservoirs have been the main target of horizontal well drilling since the early 2000s. Over the years, completion and stimulation design in horizontal wells has evolved from conservative to radical designs. It has also progressed from exploration mode to full development, and from single-well pads to multi-well pads and stacked laterals. In field development mode, infill drilling between pre-existing wells that have been on production for some time is typically done. Production interference has been observed to occur and known to have negative impact on pre-existing (parent) wells. The parent well would cause reservoir depletion resulting in localized “pressure sinks” that can cause the infill (child) well’s hydraulic fractures to grow towards the pressure sink and damage the parent well. ln addition, the production potential of the child well is likely to decrease because of the pressure sinks (depleted area). The main purpose of this paper is to understand the impact of different well spacing configurations on well interference and production performance in unconventional reservoirs. This paper is an extension of a previous work presented by Ajisafe et al. (2016) on the use of discrete fracture network (DFN)from seismic data for complex fracturing modeling.
A multi-disciplinary integrated workflow was applied in a multi-well pad, with an extensive dataset consisting of seismic, high-tier vertical and horizontal logs and microseismic data. The multi-well pad consists of two wells, a parent well that has been completed and put on production for a year, and a new (child) well to be completed on the same pad. Two different well spacings were investigated, at 660 feet and 1,320 feet to understand the negative impact of interference on the parent well production, as well as the performance of the child well due to reservoir pressure depletion of the parent well. To mitigate/avoid the negative impact of production interference on the parent well and to improve performance of the child well, the child well was landed deeper in the Avalon shale.
The DFN model and geomechanical properties were key inputs into understanding the complex fracture geometry constrained with microseismic data for the parent well. Seismic data provided an improved DFN model along and particularly away from the wellbore. The different models are discussed in detail in Ajisafe et al. (2016). The reservoir pressure depletion pattern and complex fracture geometry were then used as key input into a geomechanics simulator for an updated in-situ stress state at 1 year, which was then used for complex fracture modeling of the child well. The effect of a year of production-induced depletion on the parent well shows a change in the reservoir pressure, horizontal stress magnitude and maximum horizontal stress azimuth. Reservoir simulation was done to quantify production performance of both the parent and child wells at the different spacing configuration.
Complex fracture modeling reservoir simulation and geomechanical models in unconventional shale reservoirs are instrumental in understanding the impact of natural fractures and hydraulic fracture placement on final well productivity in multi-well pad scenarios. The optimal well spacing and completion design to maintain and/or increase hydrocarbon production with the right amount of resources is critical for maximized returns. Multi-well modeling is an important first step in the unconventional reservoir workflow, which improves planning for multi-well pad and future infill well development.