四川盆地涪陵地区龙马溪组含气页岩段上部气层平面非均质性特征及其发育主控因素

Plane Heterogeneity Characteristics and Main Controlling Factors of Development of Upper Gas Layer in Gas-Bearing Shale of Longmaxi Formation in Fuling Area,Sichuan Basin

涪陵地区五峰组‒龙马溪组底部发育一套富有机质页岩,依据页岩品质、含气性将该套页岩储层纵向上细分为9个小层,并明确下部①~⑤小层优质含气页岩段为主力开发层系.2017年,焦石坝区块针对龙马溪组一段上部中低品位页岩气层(⑥~⑨小层)启动了分层开发调整工作并取得了较好成效,但是上部气层页岩品质及厚度在平面上具备较强的非均质性,影响了分层开发调整工作的正常推进.通过对海底古地貌、水动力条件等开展系统研究,明确了上部气层的平面非均质性特征及其发育主控因素.上部气层自涪陵地区南部和北部向中部梓里场‒白涛地区由混合页岩相(粘土和陆源石英二元混合)转变为长英质页岩相(岩矿以陆源长英质为主)和粘土页岩相,页岩品质略有变差,中部梓里场‒白涛地区的北缘和南缘⑦小层出现明显减薄,普遍缺失上半段;同时在部分井区缺失⑦~⑨小层,缺失区呈现北东向条带状展布.构造火山活动、海平面升降、海底古地貌、陆源供给及底流沉积作用共同控制了上部气层的平面非均质性展布特征.

A set of organic-rich shale was well-developed at the bottom of Wufeng Formation-Longmaxi Formation in Fuling Area.Based on shale quality and gas-bearing property,this shale reservoir can be vertically subdivided into 9 sublayers,and the lower①‒⑤sublayers of high-quality gas-bearing shale are the main layers of development.In 2017,the layering development and adjustment were launched in Jiaoshiba Block,focusing on the upper middle-and low-grade shale gas layers(⑥‒⑨sublayers)of the first member of Longmaxi Formation.Good results have been achieved through this work.However,this layer has strong plane heterogeneity in terms of quality and thickness,hindering its layering development and adjustment.In this paper,we present a systematic study on the submarine paleogeomorphology and hydrodynamic conditions.Its plane heterogeneity characteristics and main controlling factors for development are clarified through systematic research.The upper gas layer changed from mixed shale facies in the southern and northern Fuling Area to felsic shale facies in the central Zilichang-Baitao area.The shale quality became slightly worse in the central Zilichang-Baitao area.The⑦sublayer on the south and north margin of central Zilichang-Baitao area showed a distinct decrease in thickness and its first half was absent.Meanwhile,the⑦‒⑨sublayers were also absent in some well regions presenting NE-trending banded distribution.Tectonic volcanism,sea level eustacy,seabed paleogeomorphology,terrigenous input and bottom currents jointly controlled the plane heterogeneity characteristics of this upper gas layer.