Abstract

During the past five years, shale gas developments have changed the game for the US natural gas industry. Globally, shale exploration activities are also increasing. China is in the early stages of exploiting the world's largest reserves of shale gas resources while attempting to cope with increasing energy demands.

This paper presents a case history of applicable technology currently used in North America for initial attempts at shale gas exploration in China. This case study is the first Cambrian age marine shale well in the Qiongzhusi formation located in the shale-gas-rich Sichuan province.

Many technologies were brought from North American shale gas applications for this well (Chong et al. 2010). This study describes the technologies used to drill and complete the targeted shale gas formation and guide the completion and stimulation design. The target formation was drilled horizontally and the casing was cemented. The formation was then stimulated with multiple stages after full integration of data from geologic, geomechanical, petrophysical, and core analysis, which aided in the fluid and proppant selection, proppant concentration, and the designed injection rate. A diagnostic fracture injection test (DFIT) was performed before the main treatment to confirm fracture gradient, closure, pore pressure, system permeability, and leakoff. Microseismic mapping was also used, which proved to be valuable when planning and assessing the fracturing results.

Currently, the well is flowing gas at rates comparable to early production time in a typical North American shale gas well with a similar type of completion.

This case study serves as an example of successful implementation of proven technology outside of the North America shale gas market. Continued projects such as this one are the predecessor to full-scale development of shale gas and have helped shape the abundant gas supply currently in the United States. Additionally, these types of projects are necessary to help China improve their future outlook on gas supply.

The Lower Cambrian Shale Location and its Geological Setting

Well Wei-201-H3 is located in Lao Chang Village, Xin Chang Town, Weiyuan County, in southern Sichuan. This was the first well targeted in the Chinese Lower Cambrian Qiongzhusi formation. According to seismic interpretation by the operating company, the Qiongzhusi formation is of high silica mineralogy and has a well-developed natural fracture network system.

The Lower Cambrian shale (Fig. 1a) is one of two promising shale horizons identified in the Sichuan basin, the other being Longmaxi. Both are thick, organic-rich, thermally mature Lower Cambrian and Lower Silurian marine shales. Preliminary data (Fig. 1b) indicates that these shales are low in clay and thus potentially favorable for hydraulic stimulation. However, the Sichuan basin's considerable structural complexity, with extensive folding and faulting, appears to be a significant risk for shale gas development.

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