Successful Cases of Horizontal-Well Tight-Sand-Gas Development in China

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 16824, ’Challenges of Horizontal Wells and Successful Cases for Tight- Sand-Gas Development in China,’ by Jia Ailin, He Dongbo, Jia Chengye, Ji Guang, and Wei Yunsheng, PetroChina, prepared for the 2013 International Petroleum Technology Conference, Beijing, 26-28 March. The paper has not been peer reviewed. Three observations have resulted from horizontal-well development in the Sulige tight gas field. First, well-location selection should be influenced by detailed geological research. Second, measurement while drilling (MWD) is the most effective technique in enhancing the drilling success rate. Third, stimulation treatments such as multistage hydraulic fracturing are the most effective way for gas wells to increase their deliverability.  Introduction Tight sand gas, one of the main types of unconventional gas reservoirs, displays the most rapid development worldwide in recent years, especially since its successful development in the US. Tight gas resources are estimated to be 10 trillion m3 in China alone. China holds a large amount of tight-sand gas resources and has obtained good performance in exploration and production during its 11th Five-Year Plan period. The Sulige gas field in the Ordos basin, the Xujiahe gas field in the Sichuan basin, and the Denglouku gas fields in the Songliao basin all show typically successful exploration and production of tight-sand gas in China. Compared with geological settings and development backgrounds in North America, tight-sand gas in China has differing characteristics, including poorer original gas in place, increased depth, and lower netpay thickness. For tight-sand-gas development, low economic benefits are the main control factor. High costs in drilling, completion, and fracturing, coupled with low revenues from wellheads, scare investors away. From a technical perspective, low saturation, low production rate, and low estimated ultimate recovery (EUR) are constraints. Thus, technical innovations to improve production level and EUR are necessary. For tight-sand gas in the US, infill drilling was the predominant development strategy in the 1990s. For tight gas wells, drainage areas are usually small, the result of reservoir heterogeneity and poor petrophysical properties. Thus, infill drilling can effectively release the remaining gas left by the primary well pattern. The consequences for infill drilling include more gas derived from the reservoir and more costs associated with drilling and completion. In recent years, horizontal drilling and hydraulic fracturing, especially staged fracturing, have become more frequent. Compared with vertical wells, horizontal wells have the advantage of greater drainage area, which can effectively increase the EUR. Staged fracturing can effectively improve the flow matrix and can increase the production rate; thus, the two main factors causing poor economic benefits and constraining tight gas development can be effectively resolved.