Construction of shallow pore pressure profile and exploration of drilling technology in karst landform areas

Abstract:

During the drilling process of shallow strata in karst landform areas， a large number of complex situations such as leakage and water inflow occur. The widely developed fracture and cave network in the strata forms fluid migration channels， and the pressure difference between drilling fluid and formation water is also an important influencing factor. Conventional pore pressure prediction methods cannot effectively characterize shallow pore pressure. To explore the actual distribution of shallow pore pressure in karst landform areas， a shallow pore pressure profile based on the actual distribution of groundwater was constructed based on hydrogeological and fluid mechanics principles. The effectiveness of the profile was verified by an exploration well drilling in west Guizhou Province. The results showed that there were multiple pressure zones in the shallow layer of karst landform areas， which were closely related to the distribution of groundwater. No pore pressure exists above the groundwater level. The calculation of pore pressure in the groundwater layer should be based on the groundwater surface， which is a typical low-pressure zone. The pore pressure of a confined aquifer depends on the difference in location between the recharge and discharge zones， and may manifest as high pressure， low pressure， or normal pressure. The adaptability of plugging materials， clean water drilling， and air down the hole hammer drilling in karst landform areas are analyzed. It is recommended to fully utilize hydrogeological data in drilling design to construct shallow pressure profiles， based on which， selecting drilling processes or drilling process combinations， and determining the depth of drilling for each drilling section to avoid complex drilling situations and improve drilling efficiency. This study can provide reference for the design and implementation of drilling projects in karst landform areas.