1887

Abstract

The accurate modeling of pre-drill, while-drilling and post-drill pore pressure and fracture gradients (PPFG) for an exploration well is a very challenging process, particularly in deep water applications. Erroneous PPFG predictions and estimations can be a source for unexpected non-productive time in drilling operations due to wellbore integrity or pore pressure related problems resulting in significant cost overruns for the well. In addition to preventing geopressure related problems while drilling, other benefits of real-time<br>PPFG modeling include identification of formation breathing, better hole cleaning, higher rates of penetration and prevention of differential sticking. This paper presents two case histories of successful PPFG modeling for deep water exploration wells in North Africa and Southeast Asia. The pre-drill PPFG models were prepared using sparse offset well data. In the drilling phases, the models were updated and calibrated based on mud weight, caving shape and leak-off test information. Eaton’s resistivity PPFG method was used to estimate the PPFG model in real-time. In addition to Eaton’s resistivity method, Matthews’ and Kelly’s method was also used in predicting the fracture gradient. A hydraulics model was run in parallel to the drilling operation, so that real-time ECD (equivalent circulating density) could be compared against theoretical values to detect anomalies and to ensure that the annulus pressure stayed within the predicted PPFG window. At the end of the drilling phase, the real-time PPFG model was found to be within 0.1 ppg of actual formation testing pressure readings. Based on the two case histories, the paper will illustrate in detail the process steps required for realtime PPFG modeling and demonstrate the benefits of taking the proper actions to mitigate risks identified by the PPFG model.

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/content/papers/10.3997/2214-4609-pdb.255.36
2010-03-29
2024-03-29
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