Multi-Bench, Multi-Well Interference in an Unconventional Reservoir: Field Observations and Numerical Studies in the Texas Delaware Basin

Abstract

Operators in the unconventional arena are endeavoring to improve project economics by optimizing well count per section, landings, spacing, and completions given the conditions of commodity price, geology, and fluid characteristics. In multi-bench developments, pressure variation and phase segregation are two of the contributors affecting well performance. This paper presents multiple observations (development cases) on how landings affect multi-bench, multi-well development and how pressure variations among benches and the phase segregation affect the performance of wells on different landings.

The field cases presented herein are sections having different landings across a large development area in the Delaware Basin (wide sample size and coverage). The sample set includes different spacings (vertically and laterally) and completion designs, making this sample set very diverse and representative for broad conclusions. These observations were combined with a comprehensive reservoir modeling study incorporating detailed geological, petrophysical, PVT, and hydraulic fracturing models to examine the relationships between different parameters.

The field observations showed inter-bench interference between shallower and deeper benches and favorable oil recovery results for the wells on the shallower bench. Our hypothesis based on these observations is that pressure variation among benches and vertical phase segregation cause the hydrocarbons in the drainage area to be preferentially produced by shallower wells. Numerical reservoir simulation analysis for multi-bench co-development and parent-child development reproduces the field observations, with relatively higher hydrocarbon recovery from shallower wells and lower recovery from the deeper wells.

The results show that pressure differences between benches and phase segregation can affect well inventory, recovery factor, and future development in this area. The recovery factor was also analyzed as a function of landing separation in primary and secondary benches. This inter-bench interaction due to pressure difference (viscous force) and phase segregation (buoyancy force) can be incorporated in development planning to arrive at optimum well spacing, both vertically and laterally, to enhance ultimate recovery. However, the optimization window is narrow, and interaction becomes net negative at tighter spacing.