Research on optimized and fast drilling technology for shale gas exploration in complex geological condition areas of Hunan

Abstract:

Hunan Province has huge potential of shale gas resources， however， controlled by the composite structure of the Yangtze Block and the Jiangnan Uplift Nappe Belt， well-developed folds and faults， extensive karst distribution， strong water sensitivity of shale formations， and frequent interbedding of hard and soft rocks are characterized in this area， leading to frequent engineering problems in deep drilling， such as lost circulation， borehole collapse， well deviation， difficult coring， poor cementing quality， and high well control risks， which severely restrict the exploration and development process. Based on data from more than 60 shale gas wells in Hunan Province， as well as the drilling practice and field tests of key wells from more than 30 shale gas wells implemented by the Hunan Coal Geological Exploration Institute， this paper systematically analyzes the engineering geological characteristics and key engineering challenges of five major gas-bearing formations in northwestern and central-southern Hunan， namely the Niutitang Formation of the Cambrian， the Longmaxi Formation of the Silurian， the Ceshui Formation of the Carboniferous， the Longtan Formation of the Permian， and the Shetianqiao Formation of the Devonian. To address the key engineering challenges of shale gas wells， a low-density expandable pressure-bearing lost circulation control technology has been developed （achieving one-time sealing of long sections with multiple loss zones）； an integrated anti-sloughing technology system of "strong inhibition+high-efficiency sealing" has been established （achieving a hot-rolling recovery rate of more than 99.6% and a 16 h expansion rate of no larger than 3.24%）； three new types of wire-line coring tools have been developed （increasing the core recovery rate from about 70% to over 90%）； a precise wellbore trajectory control technology combining PDC bit， single-bend screw motor and MWD/LWD has been developed； an integrated well control technology system of "near-balanced drilling-active throttling circulation-mud logging warning" has been established； and a complete set of cementing technologies featuring "safe casing running-high efficiency displacement-high toughness anti-channeling" has been formed （achieving a 100% high quality cementing rate）. Finally， a deep shale gas drilling construction technology system suitable for the complex geological conditions of Hunan Province has been developed， consisting of four-spud sectional drilling， graded drilling fluid maintenance， and whole-process quality control of cementing. This system has been successfully applied in more than 30 wells， providing important technical support for shale gas and other deep mineral exploration in complex geological areas of South China.