Methods For Formation Pressure Prediction Based On 3D Seismic Data

Abnormal formation fluid pressure is a high risk factor in drilling operations. As the exploration targets become even deeper, there is clearly a need for an accurate method for the pre-drill and the pore pressure prediction in the process of drilling. In the oil field drilling phase, in order to reduce the occurrence of well leakage blowout accident, make drilling cycle shorten, increase drilling speed and use drilling fluid with accurate density, we also need accurate formation pressure. Weakness remains due to(1)limitations of the seismic velocities themselves;(2)lack of understanding of the basic causes of pressure;(3)effects of pressure on physical properties(including velocity, density, and porosity) of rocks.The new method is mainly for H Bohai field. A highly precision method for formation pressure is put forward. Then the new method take the following steps to carry out the prediction.(1)It is recognized that the main reasons of the abnormal pressure in the third member of Shahejie Formation are undercompaction and flow expanding caused by source generating.(2)In order to compensate the shortage of measured pressure data, Eberhart-Phillips formula is used to calculate the data of whole formation in well, so that more well data can be used for the prediction of 3D data in the target formation. The advantages of Eberhart-Phillips formula are taking into account the impact of rock properties(velocity, porosity, clay content)on the formation pressure.(3)Using the log data, the paper fits the Gardner formula for the whole well and the target layer, then calculate its velocity in 3D data, which is called background velocity and target layer velocity. The background velocity field is calculate from the stacking velocity transfer to the interval velocity constrained by wells. The velocity of target formation is calculated by simulated annealing algorithm and Gardner formula. The background velocity reflects the trend of overburden pressure and the other is more relevant to the lithological properties of the target formation. So the accuracy can be promoted.(4)Using the Gardner formula from the entire well, the paper calculates the density from the surface to the target layer and then integrating the density to calculate the overburden pressure. Then the velocity of target layer is substituted into the Fillippone formula, obtaining 3D pressure data constrained by the pressure data from the well in order to achieve an accurate prediction of formation pressure.