Geomechanical-Evaluation Enabled Successful Stimulation of a High-Pressure/High-Temperature Tight Gas Reservoir in Western China

Abstract

SummaryThe Keshen reservoir in China is a deep, tight-gas-sandstone reservoir under high tectonic stress with reservoir pressure at more than 16,000 psi (110 MPa) and temperatures up to 165°C. Development wells for this field are in excess of 6500 m in true vertical depth (TVD). Stimulation is required to provide sufficiently high production rates that compensate for the high cost of drilling and completing wells. Hydraulic-fracture design and execution must be optimal to ensure economic production.To effectively stimulate a more-than-200-m-thick sandstone reservoir with consistently high performance, it is necessary to understand the mechanical behavior of the reservoir, especially mechanical properties and in-situ stresses because the two control the creation and propagation of each hydraulic fracture. The mechanical behavior is complicated by high tectonic stresses, significant compaction, and high overpressure.To gain an in-depth understanding of the mechanical properties and in-situ stresses of the Keshen reservoir, an integrated geomechanical evaluation was conducted. The evaluation used the core from two wells, KS205 and KS207, and log data obtained from 15 wells including the wells with core evaluation in the field. A laboratory-testing program to investigate the mechanical behavior of the reservoir sandstone under realistic in-situ stresses, pore pressures, and temperature was performed. The description of mechanical behavior obtained from the laboratory testing was used to calibrate and augment mechanical Earth models (MEMs) constructed from well-log data. The reliability of the completed MEMs was validated through comparison between wellbore-stability predictions with observation of borehole failure from the borehole-microresistivity image.The geomechanics information was delivered to the stimulation-engineering team. Hydraulic-fracture design and execution was conducted on the basis of this information. The outcome of hydraulic fracturing was very encouraging.This study demonstrated that successful stimulation of a tight reservoir in high pressure/high temperature (HP/HT) relies on integrated geomechanical analysis.