The Study & Application of Maximizing Fracture Height Penetration and Complexity Through Stratified Lithology in Lacustrine Shale Gas Play in Sichuan Basin, China
Authors: Tingxue Jiang , Bo Xiao , Changgui Jia , Qiuping Qin , Jun Zhou , Xiaobing Bian , Luo Zuo , Xiaoyang Wang 
Published: October 2022

Abstract
Nowadays, with the breakthrough of hydraulic fracturing in marine shale gas play, the annual production reached 20 billion cubic meter in the year of 2020. However, it is not enough to satisfy the demand of ever-increasing economy of China. So that other kinds of lacustrine shale gas must be developed economically. However, there are many challenges in hydraulic fracturing such as confined fracture height penetration as a result of stratified lithology, less complexity as a result of bigger horizontal stress difference (&gt;10 MPa) and higher clay content (&gt;50%), higher stress sensitivity and clay expansion so as to cause higher fracture conductivity damage ratio. Accordingly, new strategies and countermeasures were put forward as followings: 1) maximizing fracture height penetration vertically through the stratified lithology by virtue of higher viscosity gel in pre-pad injection and using directional perforation technique;2) adopting acid plugging or acidic slick water, using temporary plugging agent within fractures and decreasing distance between adjacent clusters as well, and 3) developing longer effective clay stabilizer, mechanism study and control of fracture face compaction and flowing back (imbibition under high pressure), and increasing proppant weight or intensity as soon as possible, etc. Furthermore, above research achievements were applied and tested in more than 8 pilot wells, and the results indicated 100% fracturing treatment success, on the other hand, the vertical fracture height growth and complexity were both improved a lot (&gt;30%, &gt;20%, respectively) than ever before, and 4 wells obtained an expected performance, which brings a beam of light in economically develop lacustrine shale gas play in the near future. Therefore, it has a great significance in the study and implement of hydraulic fracturing stimulation in the similar shale gas all over the world.

Introduction
With the success of horizontal well staged fracturing technique in marine shale gas play in China in the past decade, its most recent development mainly focusing on densely distributed perforation clusters, high proppant intensity as well as temporary plugging either with balls in horizontal wellbore or granular agents in main fractures (Tang et al., 2011). However, when we adopted above strategies in lacustrine shale gas play, it did not always work. For example, using higher and higher pumping rate is feasible in marine shale gas wells while using the same technique in the lacustrine ones, the fracture face compaction as a result of high clay content may play a key role in reducing permeability dramatically so as to prevent shale gas flowing from rock matrix to fractures after fracturing treatment job (Dennis D, 2016). In other words, high pumping rate may cause high bottom hole pressure and high compaction effect on surface of fractures correspondingly. Therefore, the positive effect of high pumping rate may be offset greatly by its negative one.