Geo-steering technology for horizontal wells in deep karst Dengying reservoirs of the Gaoshiti gas field, Central Sichuan Basin

摘要

The Upper Sinian Dengying formation in the Gaoshiti gas field, Central Sichuan Basin, has always been the major payzone of natural gas exploration and development in this basin up till now. But due to the complexity of siliceous and heterogeneous reservoirs there such as high temperature, high pressure, high H2S content, well-developed pores and fractures, frequent sticking and leakage often occur along with high risks of blowout during horizontal-well drilling, which even makes geo-steering, and reservoir tracing and orientation difficult. In view of this, based on the analysis of geological and drilling characteristics of Dengying reservoirs and the summary of actual drilling data, we put forward a geological modeling technology for multi-well lithofacies interpretation and reservoir comparative analysis, fracture-cavity detection through comprehensive logging, geology and seismic data; then bycombining the real-time geo-steering technology of reservoir identification with evaluation with LWD data, reservoir seismic model and cutting element analysis, we focused on the optimization of such aspects as the inclination angle at the top of Dengying Fm, the trajectory plan for the build-up section, the suitable string and the directional operation scheme, and the well trajectory technology for avoiding siliceous and tight layers, and finally formed an integrated geo-steering technology suitable for the geological and engineering characteristics of the Dengying reservoirs. The field practices of five wells show that this presented method is worth popularizing in that the drilling goal with geological guidance has been achieved; that effective reservoir drilling rate and drilling efficiency have been increased; that operation risks have been reduced; and that the needs of geological guidance under complex geological and borehole engineering conditions in this area have been met.