FORMATION FRACTURE PRESSURE PREDICTION

ABSTRACT

Formation fracture pressure is a key element in the pre – design stage of deep wells, hydraulic fracture program and reservoir management. Improper planning and execution of drilling operations may lead to disaster/damages. Unfortunately, however, accurate prediction of fracture pressure can be very difficult especially in deep abnormal pressure formation and where the area of interest is dominated by irregular lithological behavior. Simple prediction models such as Hubert and Willi (1957), Eaton (1969), Matthew and Kelly (1967), Pennebaker (1968) and Macpherson and Berry were adopted to predict the fracture pressure of the formation at various depth and the results obtained from the models were compared to that of LOT. The result of LOT at depth 7072ft using a mud weight of 9ppg gave a leak off pressure of 4949.696psi. is greater than the leak off pressure and did not meet the LOT curve. After correcting the model A combination well log (CWL) was conducted and the bulk densities of the fluid occupying the pore spaces were recorded at various depths and were used to calculate the equivalent overburden pressure in ppg and psi. An average pore pressure gradient of 0.465psi/ft was assumed in order to calculate for the pore pressure (psi). Upon analysis of obtained results, Ben Eaton’s model has a fracture pressure of 4950.5psi which is 0.8psi more than leak off pressure (LOP), Hubert & Willis has a minimum fracture pressure of 4995.7psi which is 46psi more than leak off pressure (LOP), Matthew & Kelly has a fracture pressure of 7104.1psi which is 2154.4psi more than leak off pressure (LOP), Pennebaker has fracture pressure of 7027.33psi which is 2077.63psi more than LOP and Macpherson and Berry gave 6195psi Indicating that Ben Eaton’s model best describe the pressure profile of ABOR field . Also, the Matthew and Kelly model which is applicable to Gulf Coast, was modified to suit the Niger Delta field under study by introducing the constants � and � which tend to shift the curve for Matthew and Kelly to fit with LOT curve using the LOT value as minimum constraint. Before correction, it can be seen that the fracture pressure from Matthew and Kelly model, figure 3.6 shows that case 1 was closer to the LOT curve compared to case 2.