Analysis of key elements affecting production and technical countermeasures to increase production of CBM fractured single horizontal wells:a case study of Zhengzhuang Block
ZHANG Chen;HE Meng;XIAO Yuhang;LIU Zhong;HAN Sheng;LU Xiuqin;WANG Zihan;WU Haoyu;ZHANG Qianqian
单支压裂水平井作为沁水煤层气田煤层气开发主体技术,支撑了气田20亿m3/a产气量的突破。但在其规模推广应用过程中,出现井间产量差异大,局部区域适应性欠佳等系列问题,严重制约了气田煤层气产量进一步提升。一方面,众多影响单支压裂水平井产气量的关键要素已被确认,但核心关键要素却不明确;另一方面,关键要素的平面变化规律认识,普遍为简单数学外推或纯粹数学反演,缺少地质约束和修正,可靠性和分辨率低。故亟需落实影响产量核心关键要素,以此为基础建立针对性提产技术对策。首先,基于郑庄区块客观地质条件和开发生产实践认识,提出影响单支压裂水平井产量的核心关键要素初步筛选原则,并评选出纯煤层进尺、水平段倾斜幅度、全烃、GR(自然伽马)、压裂段数、平均砂量梯度、平均排量梯度、平均液量梯度、解吸压力梯度9项要素。用灰色关联分析和单因素分析方法,明确初筛9项要素与单支压裂水平井产气量间的关联程度,落实要素对产量影响的内在机制。其次,从资源基础、储量控制和改造动用3个角度,结合单支压裂水平井部署和改造设计和施工具体流程分类9项要素,并依此建立针对性的提产技术对策。在井位部署阶段,利用评价井外推资料,初步明确相对富集区域,用构造导向滤波+高频相干技术处理地震资料,圈定无隐蔽性破坏构造发育区,再钻直/斜井以获取煤层段GR和全烃,落实井位部署区资源基础;在井轨迹设计和钻井阶段,利用波形聚类技术预测井位部署区内构造煤分布规律,对地震资料叠前深度偏移处理预测井位部署区内煤层厚度和起伏变化规律,用井组模式,分批次钻井,结合近钻头地质导向技术,实钻数据实时修正局部煤层认识,增加纯煤层进尺,优化井轨迹,确保更多优质压裂段,提高储层控制;在储层改造阶段,通过GR、全烃、井轨迹条件和实钻数据等优选压裂段,采用桥射联作压裂技术提升排量、砂量和液量,扩大改造规模,强化改造,提升资源动用程度。最后,运用上述对策在郑庄区内开展相关试验,在郑庄北部部署1个井组7口井,与周边早期单支压裂水平井相比,试验井较之前解吸压力高出约1~1.5 MPa,稳产气量提高近5 000~10 000 m3/d。该研究评选了影响单支压裂水平井产气量的核心关键要素和以此为基础而建立的针对性提产技术对策,经现场试验检验,能大幅提高煤层气井稳产气量和解吸压力,为沁水煤层气田产量提升和采用相同主体开发技术的同行提供生产实践经验和可借鉴的成功案例。
As the main technology of CBM development in the Qinshui CBM field, single-branch fractured horizontal wells have supported the breakthrough of 2 billion m3/year production of gas field. However, in the process of its large-scale application, there have been a series of problems, such as large difference in production among wells and poor adaptability in local areas, which seriously restrict the further improvement of CBM production in gas fields. On the one hand, although many key elements affecting the production of single-branch fractured horizontal wells have been identified, the core key elements are not clear. On the other hand, the understanding of the change rule of key elements on the plane is generally simple mathematical extrapolation or pure mathematical inversion, which lacks geological constraints and corrections, and has low reliability and resolution. Therefore, it is urgent to clear the core key elements that affect the production, and then establish targeted technical countermeasures on this basis. First of all, based on the objective geological conditions and the understanding of development and production practice in the Zhengzhuang block, the preliminary screening principle of the core key elements affecting the production of single−branch fractured horizontal wells was proposed, and nine elements were selected, including drilling length in pure coal seam, horizontal section inclination, total hydrocarbon, GR, number of fracturing stages, average sand gradient, average displacement gradient, average fluid volume gradient and desorption pressure gradient. Then, grey correlation analysis and single element analysis were used to determine the correlation degree between the nine elements of the preliminary screening and the production of single−branch fractured horizontal wells, and determine the internal mechanism of the elements' influence on the production. Secondly, from the three perspectives of resource base, reserve control and reconstruction, combined with the specific process of a single-branch fractured horizontal well deployment, reconstruction design and operation, nine elements were classified, and targeted technical countermeasures for production enhancement were established. In the stage of well location deployment, extrapolation data based on evaluation wells were used to initially identify the relatively enriched area, and the seismic data were processed by structure-oriented filtering + high−frequency coherence technology to delineate the local area for clearing hidden destructive structures in the area, and then straight/inclined wells were drilled to obtain GR and total hydrocarbons in the coal seam segment to determine the resource base of the well location deployment area. In the stage of well trajectory design and drilling, the waveform clustering technology was used to predict the distribution law of strongly deformed coal in the well location deployment area. The pre−stack depth migration of seismic data was processed to predict the thickness and fluctuation change law of coal seam in the well location deployment area, the well group mode was used to drill in batches, and the near−bit geological guidance technology was combined with the real drilling data to correct the local coal seam understanding in real time, to increase drilling length in pure coal seam, optimize well trajectory, ensure more high−quality fracturing stages, and improve reservoir control. In the reservoir reconstruction stage, GR (Gamma Ray), total hydrocarbon, well trajectory conditions and real drilling data were used to select fracturing stages, and the joint operation techniques of bridge plug setting, shooting and fracturing was used as a new fracturing technology to increase the displacement, sand and fluid volume, increase the reconstruction scale and strengthen the reconstruction, and improve resource utilization. Finally, relevant tests were carried out in the Zhengzhuang block by using the above countermeasures. A well group with 7 wells was deployed in the north of Zhengzhuang. Compared with the early single-branch fractured horizontal wells around the well group, the desorption pressure of the test wells is about 1-1.5 MPa higher than before, and the stable gas production is increased by nearly 5 000-10 000 m3/d. According to field practice tests, the core key elements affecting the production of single-branch fractured horizontal wells and the targeted production technical countermeasures established on this basis can greatly improve the stable gas production and desorption pressure of coalbed methane, which can help improve the production of the Qinshui coalbed methane field and provide important production practice experience and successful cases that can be learned from for peers who adopt the same main development technology.
single-branch fractured horizontal well;factors affecting coalbed methane production;grey rational analysis;single factor analysis;technical countermeasures of increasing CBM production;field pilot test
主办单位:煤炭科学研究总院有限公司 中国煤炭学会学术期刊工作委员会