Geomechanical Evaluation Enabled Successful Stimulation of a HPHT Tight Gas Reservoir in Western China

Abstract

Keshen reservoir is a deep, tight gas sandstone reservoir under high tectonic stress with reservoir pressure over 16,000 psi (110 MPa) and temperatures up to 165 °C. Development wells for this field are in excess of 6500m in true vertical depth. Stimulation is required to provide 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 behaviour of the reservoir, especially mechanical properties and in-situ stresses as the two control initiation and propagation of each hydraulic fracture. The mechanical behaviour 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 Keshen reservoir, an integrated geomechanical evaluation was conducted. The evaluation used 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 based on this information. The outcome of hydraulic fracturing was very encouraging.This study demonstrated that successful stimulation of tight reservoir in high pressure, high temperature relies on integrated geomechanical analysis.