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Abstract:
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There are many complications associated with abnormally high fluid pressures in overpressured formations . Pore pressure can directly influence all parts of operations including drilling , geological studies , completion , and production . Accurate predictions of pore pressure and fracture pressure are vital aspects to the production and completion of safe , time efficient , and cost efficient projects . Knowledge of pressure distribution in the formation can greatly reduce complexities associated with drilling and completing a well .
A three -method pore pressure and fracture pressure study was performed on two prospect deepwater wells located in the Gulf of Mexico . More than thirty offset wells in the greater region were initially analyzed for similarities with the two prospect wells . In the final analysis , only six wells were used to create pore pressure and fracture pressure models due to inconsistencies in similarities or lack of usable data in many of the offset wells . Pore pressure and fracture pressure models were constructed for the offset wells , and then applied and calibrated for the two prospect wells using drilling data such as mud weights , MDTs (Modular Dynamic Testing ) , and LOTs (Leak -off Test ) . Three types of pore pressure and fracture pressure models were used in the study : Eaton’s deep resistivity method ; Eaton’s acoustic sonic method ; and Bower’s interval seismic velocity method .
Pore pressure and fracture pressure prediction was complicated by abnormal pressure in the formation due to undercompaction and seals . Both prospects were located in a deep subsalt environment . Low permeability and traps prevents fluid from escaping as rapidly as pore space compacts thus creating overpressure . Drilling through salt in deep water is expensive and risky . Elevated pore pressure and reduced fracture pressure underneath salt seals can create very tight mud weight windows and cause many drilling problems , as seen in the results of the offset wells’ pore pressure and fracture pressure models .
Results indicate very small pore pressure and fracture pressure windows , or mud weight windows , because of overpressures in the formation caused by such a deep subsalt environment . Many casing points were needed in the final casing design of prospect wells to accommodate the smaller mud weight windows . Pore pressure has the most significant increase immediately below the salt , while the mud weight window remained constant or decreased with depth . The average mud weight window ranged between 1 to 2 pounds per gallon below the salt . |