Case Study: A Challenging Large-Scale Fracturing In Sichuan Basin
Authors: Yuan Feng , Wang Kai , Blanton Eric , Zeng Winston 
Published: March 2015

The success of commercial production of shale gas/oil in North America encourages other countries, such as China to replicate the U.S. shale gas revolution. The Sichuan Basin located in southwest of China is one of the largest proven shale formations with complex tectonics compared with US shale plays. The shale has natural fractures and local Earth stress is complex. The high formation stresses make initiating hydraulic fractures difficult. Therefore, very high surface fracturing pressure and high horsepower is needed to perform large scale fracturing jobs and initiate hydraulic fractures.

There are two types of shale formations in the Sichuan Basin, one is a lacustrine formation that is not a common formation globally to produce hydrocarbons and the other a marine formation. A couple of appraisal wells have been successfully drilled and fractured with commercial gas production rates in both formations. One horizontal shale gas appraisal well in the lacustrine formation was drilled with 4,102 meters (13,454ft) in total measured depth (MD), 3,088 meters (10,129ft) in true vertical depth (TVD) and 815meters (2,673 ft) in horizontal section. The 10-stage ball-activated sleeves and open hole packers system were chosen as the multistage fracturing completion design. Based upon the research and analysis of this formation, the largest ever shale gas frac operation in China was completed in January, 2013. A total of 265.7m3 (990,000lbs) of proppant and 8625.5m3 (2,278,616 gals) of frac fluid were pumped into the target formation with a maximum surface fracturing pressure of 61MPa (8,847psi) and a pump rate of 12.4 m3/min (77.9 bbls/min). This frac operation set 2 new records in China for the proppant tonnage and the frac fluid volume.

This paper will provide a comprehensive view of this successful fracturing operation in the lacustrine formation including formation evaluation, fracturing design and fracturing completion strategy such as determining the optimal number of frac stages per lateral, proppant type and mesh size, volumes of proppant pumped on each stage, fracture completion tool, fracturing fluid type, and injection rate. The success of the fracturing job in this well marks a new breakthrough in gas field exploration in the Sichuan lacustrine formation and provides a guideline for future shale gas frac operations in similar formations or blocks.

Introduction

Due to rapid development in the last few decades, China is one of the most energy hungry countries in the world. To date, China is still heavily reliant on coal for energy which severely affects pollution, emissions and efficiency. To address these problems, the government has become more and more aware of the need to change energy consumption composition, i.e. reduce coal usage and increase use of natural gas. What is important is that China has great potential for natural gas production, especially for shale gas.

In China, compared with marine formations from which a large amount of oil and gas has been produced, very limited attention has been paid to lacustrine formations, such as the Xujiahe formation in Sichuan Basin where there exists good conditions for potential commercial reservoirs. As the shale gas industry in North America has successfully developed and been leading the world, learning from North America is a good choice to accelerate shale gas development for China. Based on these considerations, the well in this case study was intended to be drilled as one of appraisal wells to find out the commercial production potential of the Xujiahe formation and execute a multistage hydraulic fracturing based on applying US technology and experience.