Abstract

After dozens of exploration and appraisal wells were drilled, fractured and tested in the Lower Silurian Long Ma Xi (hereafter referred to as LMX) shale formation in Sichuan basin since 2009, several blocks have now entered into the development phase. Hydraulic fracturing stimulation is vital to the performance of shale gas wells as well as the economics since it represents about half of the total well cost. Aiming at increasing production, most operators focus on enlarging Stimulated Rock Volume (SRV), a common means for which is to increase the injected fluid volume. Whilst injecting more fluid will lead to an enhanced SRV during the fracture stimulation process, how much of it is effective SRV under closure stress is often unknown and tends to be field specific. It is possible that a large portion of the injected fluid and consumed energy is actually ineffective in terms of adding more production rate.

Based on some early production data of wells in Fushun-Yongchuan (herein after refer to as Fushun) block and its sensitivity analysis to completion parameters, it is found that the amount of injected fluid volume does not obviously impact the performance. Instead, proppant intensity; the volume of 100 mesh natural sand carried by slick water; and proppant pack continuity are all more important variables. These variables are not generally the focus of most operators in the area. A concept for improving the effective or propped SRV is developed as a result, with key points summarized as below:

  1. Significantly reduced frac fluid volume compared to original base design;

  2. Enhanced proppant intensity;

  3. Significantly increased 100 mesh sand volume;

  4. Continuously adding proppant to achieve best proppant pack continuity at fracture face;

  5. Tailored frac fluid design to meet the proppant transportation needs meanwhile minimize the residue damage

The above concept has been put into field trials in Fushun area. Field execution went well and demonstrated higher efficiency in terms of operation time, however did require a higher level of onsite QAQC and real-time engineering control. Early production data has been gathered and analyzed to assess the performance impact of this approach, indicating that a consistent performance improvement has been observed. This new shale gas frac concept is practical and beneficial on both operational efficiency and well stimulation performance.

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