Chevron has performed surveillance, analysis and optimization (SA&O) pilot study in its Midland Basin Wolfcamp tight oil development area. In this paper, we will focus on the pilot overview, production logs, rate transient analysis (RTA), and multiple well interference pressure transient analysis (PTA).
The pilot area consists of a center 20-acre vertical well and four pressure monitoring wells in four directions with a distance of 460 ft to the center well. Production is commingled by 8 hydraulically fractured stages. Four-array downhole microseismic shows the shape of reservoir stimulation. Each vertical monitoring well is equipped with 8 permanent downhole gauges with packers isolating 8 layers, and the real-time data is acquired through SCADA (Supervisory Control and Data Acquisition) system. Multiple production logs have been acquired in the center well during the earlier natural flow period.
RTA has been performed in the center well based on the production rate measured from a dedicated test separator, flowing bottomhole pressure from a downhole memory gauge, and zonal contributions from production logging (PLs). PLs show that fluid comes primarily from the Spraberry, secondly from the Lower Wolfcamp, and some from the Strawn and Atoka. The RTA shows that effective drainage area of the well is less than 20 acres. In addition, fracture half-length and effective permeability are degrading with time, which impacts the well's EUR. The acquired pressure responses in observation wells have been studied with non-linear numerical model in PTA to better characterize the fracture network and reservoir. It shows a high possibility of connecting with neighbor wells in certain formations and exhibiting characteristics of time-dependent fracture closing. Production performances with original 40-acre spacing wells and recently drilled 20-acre infilled wells are compared, indicating that 20-acre wells helps to improve oil recovery and economics. The center well was shut in for more than 9 months to get buildup data. During the 5 month post shutin production (PSP), the well had significantly higher oil rate and positive net oil recovery with decreased GOR and water-cut.
The pilot sheds light on first principles and tight oil development strategy. Accurate microseismic data, production logs, interference well testing, and rate transient analysis are powerful tools for unconventional studies.