Simulation Study on Reservoir Stimulation of Multihorizontal Wells for Gas Hydrate Production in Low-Permeability Reservoirs
本文针对低渗透储层中天然气水合物开采效率低下的问题，提出了四种不同的多水平井开采方案并建立了模拟模型。研究了储层改造和水平井偏移距离对水合物解离、饱和度变化和压力分布的影响模式，并探讨了多水平井的耦合效应。通过模拟得出以下结论：
（1）储层改造能有效提高产气量，在四种开采模型中，330天内C方案（多水平井+储层改造）的累计产气量是A方案（仅多水平井）的5.27倍，而D方案（带筛管完井）的产气量比C方案减少15.58%；
（2）水平井不同偏移距离对累计产气量和日产气量影响较小，但水合物饱和度变化范围随偏移距离改变，表明水合物解离主要集中在水平井和裂缝周围；
（3）考虑井间耦合，内井的日产气率和累计产气量高于外井，330天内累计产气量增加6.4%。时空上，井间水合物饱和度变化显著快于水平井向外扩展，且越靠近水平井轴线，水合物饱和度变化越明显。这些结果可为优化海洋水合物多水平井开发提供理论数据。
CMG软件应用情况：
本研究采用CMG STARS软件进行水合物开采模拟，通过添加水合物生成和分解反应的动态方程来模拟水合物开采过程。模拟中考虑了水合物储层的多相流和传热传质过程，包括气、液、固三相的平衡关系、水合物的相平衡反应、渗透率变化以及毛管压力计算等。通过设置不同的开采方案和参数，模拟了多水平井在低渗透储层中的开采性能，并分析了储层改造和井间耦合效应对水合物解离和产气量的影响。
Abstract
The feasibility of hydrate exploitation technology has been verified by two rounds of trial productions in the South China Sea, but it is also faced with the problem of low gas production efficiency. Therefore, this paper proposed four different hydrate production cases with multihorizontal wells and established simulation models. Then, the influence patterns of reservoir stimulation and offset distances on hydrate dissociation, saturation change, and pressure distribution were studied. To understand hydrate dissociation behaviors and production performances, the coupling effects of multihorizontal wells were discussed. Through simulation, the following conclusions could be drawn: (1) hydrate reservoir stimulation could effectively increase gas production. In these four production models, the cumulative gas production in Case C (multihorizontal wells + reservoir stimulation) was 5.27 times that of Case A (only multihorizontal wells) in 330 days. However, in Case D with screen completions, the gas output was 15.58% less compared with Case C. (2) Different offset distances of horizontal wells had a relatively minor impact on the cumulative gas yield and daily gas capacity. In addition, the variation range of hydrate saturation changed with offset distances of horizontal wells, indicating that hydrate dissociation occurred mainly around horizontal wells and fractures. (3) Considering interwells coupling, the daily gas rate and cumulative gas production of inner wells were higher than outer wells, and the cumulative gas volume increased by 6.4% in 330 days. Temporally and spatially, the hydrate saturation variation between wells was significantly faster than the outward expansion from the horizontal wells. Moreover, nearer to the axis of the horizontal wells, the variation in the hydrate saturation was more pronounced. These results could provide theoretical data to optimize marine hydrate development with multihorizontal wells.
作者单位：
中国地质科学院
