Key technologies and orientation of EGR for the Sulige tight sandstone gas field in the Ordos Basin

Abstract

The Sulige Gas Field in the Ordos Basin is the largest tight gas field in China, with proved reserves exceeding 2 × 1012 m3. As the main contributor to gas production in PetroChina Changqing Oilfield Company, The Sulige Gas Field is in the stage of stable production. Maximizing the stable production period is a focus and challenge for the gas field now. To address a series of problems influencing the efficient development of Sulige gas field, such as large-scale remaining gas reserves between wells/layers and low ratio of employed reserves, the main technologies for enhanced gas recovery (EGR) of tight gas reservoirs were developed by multidisciplinary research with respect to development geology, reservoir engineering, drilling and production process, and surface gathering and transportation. Experiments were conducted on reservoir description and remaining gas characterization, well pattern thickening optimization, vertical well separate-layer fracturing, horizontal-well multi-stage multi-cluster volume fracturing for their improvement and upgrading. The orientation of EGR for tight gas reservoirs is proposed. The following results are obtained. First, well pattern thickening optimization is the most important EGR method, which can increase the recovery rate by more than 6%. Second, based on continuous upgrading and promotion, either of reservoir stimulation technology and drainage gas recovery technology can increase the recovery rate by more than 2%. The gathering and transportation technology which further reduces the wellhead pressure can increase the recovery rate by about 1.5%. Third, the EGR technology should be oriented to maximize the quantity of employed reserves, especially by way of new technologies such as fine remaining gas characterization, well pattern/type optimization, cross-layer fracturing of a multi-thin-layer reservoir by horizontal wells, intelligent drainage gas recovery, and multi-stage pressurization. It is concluded that the development of key EGR technologies will help increase the recovery rate of The Sulige Gas Field by 10%–15%, and will provide an effective support for The Sulige Gas Field to maintain the production at 300 × 108 m3/a for a long term and for the Changqing gas province to increase the production to 500 × 108 m3/a, which will ultimately ensure the national energy security.