The Application of Seismic while Drilling in High Temperature, High Pressure Reservoirs of the Yinggehai Basin

There are high temperature, high pressure (HTHP) formations in the Yinggehai Basin in the South China Sea, and they are considered high-risk for safety when penetrating the HTHP formations. In order to reduce the drilling risk, it is necessary to accurately predict the pressures and at each formation depth. For this reason, the seismic while drilling technology was applied in the pre-exploration Well DF-X1. The technology uses seismic data while drilling to obtain the time-depth relationship and the formation velocity, and it updates the bit position on the seismic profile in real time, and thus it determines the high pressure reservoir depth and formation pressure coefficient in front of the bit. During the actual drilling of Well DF-X1, the seismic while drilling technology was used to accurately predict the pore pressure coefficient, fracture pressure coefficient and depth of the high pressure reservoir A1 sand body. The predicted depth error of A1 sand body was only 6.00 m with the actually drilled depth, which ensured that the ϕ244.5 mm casing was run into the mudstone above the high pressure reservoir. By using seismic while drilling, the prediction accuracy of A1 sand body pore pressure coefficient achieved 3.0%, and the accuracy of formation fracture pressure coefficient up to 1.0%. Based on this, the drilling fluid density of the completion section was optimized to avoid the gas cut and lost circulation, kept the successful drilling of the well. The research results showed that the seismic while drilling technology could accurately predict the formation pressure along with the depth of the targeted high pressure reservoir, thus effectively reduce drilling risk and improving operation efficiency.