Pressure gradient computation and application of the wireline formation tester

One function of the wireline formation tester is to calculate pressure-depth gradient line (pressure gradient) from testing data. Its application is limited resulting from the uncertainties in the computational method, which often results in a big deviation. The effect of the reservoir thickness, the effective measuring point number, and the measurement error distribution of pressure-measuring points on the computational precision of pressure gradient was studied by numerical simulation: the thicker the measured reservoir, the more the measuring-point number, and the closer the measurement errors of all measuring points are, the higher the computation precision is. The selection of measuring points should take into account fluid character, formation pressure coefficient, reservoir connectivity, and so on. Pressure gradient can be applied in the analysis of the fluid property, the oil and water interface, the vertical connectivity of reservoirs, the pressure systems, the vertical change of formation fluid in single wells, and in the assistant evaluation of reservoirs in multiwells.