木里地区水合物钻孔井壁构造裂缝特征

Characteristics of fractures from borehole walls of gas-hydrate drilling holes in Muli region

木里地区三露天井田断层发育、岩性复杂,且钻探结果揭示水合物主要赋存于地层裂缝中,因此,笔者专门利用声成像测井资料对三露天井田水合物钻孔井壁构造裂缝进行研究,明确了研究区构造裂缝的成像测井响应特征,并从裂缝线密度、倾角、倾向等方面对裂缝的分布特征进行了分析讨论。结果表明:(1)研究区水合物钻孔井壁裂缝发育,倾角以高角度为主,低角度次之,水平裂缝与高角度裂缝少见;冻土层及以上裂缝较冻土层以下更为发育。(2)研究区裂缝主要走向与地层断裂走向基本一致或小角度斜交,裂缝的发育受断层控制明显。(3)研究区裂缝倾角相对较大,不利于烃类气体的大量聚集,这可能是该区域钻孔少见水合物的原因之一。

Well-developed faults and diversified lithology constitute the features of Sanlutian well field, and the drilling results reveal that gas hydrate mainly occurs in the fractures of reservoirs. Therefore, the acoustic image logging data are used specifically to study the structural fractures from borehole walls of gas-hydrate drilling holes in Sanlutian well field. In this paper, the response characteristics of fractures in acoustic image logging were confirmed and the linear density, dip angle and dip direction of fractures were discussed. Some conclusions have been reached:① Fractures are developed in the borehole walls of gas-hydrate drilling holes. In these fractures, high-angle fractures are dominant, followed by low-angle fractures, and the vertical and horizontal fractures are rare.②The main strike of fractures is basically consistent with the fault strike or oblique-crossing at small angles. The distribution of fractures is controlled distinctly by faults.③It is unfavorable for the assembly of hydrocarbon gases as the fractures of the study area are dominated by high-angle fractures, which is one of the possible reasons why gas-hydrate is rare.