Wellbore Stability Issues in Today’s Challenging Development Wells
Terry Hemphill1, Daniel Simao2, and William Duran3
1Halliburton, Houston, TX
2Sonangol, Luanda, Angola
3Halliburton, Luanda, Angola
With the accelerating drive to maintain or increase production rates, the need to emphasize wellbore stability (WBS) issues as key elements of longtime well productivity is even more paramount. Maintaining adequate wellbore stability in a producing well is at times not an easy task, especially given the fact that other issues interplay with wellbore stability. Wellbore hydraulics, long considered as issues for calculation of circulating pressure drop and hole cleaning, can now be better understood as a complement of wellbore stability.
In this paper, key drivers of hydraulics that can have consequences for wellbore stability include:
1. The role of Equivalent Circulating Density
2. The need for downhole density modeling for invert emulsions drilling fluids
3. Formation destabilisation caused by hydraulic swab
4. The effect of circulating hydraulics on weak formations
The integration of hydraulics with wellbore stability was performed for a deepwater Angola project. The operator had commissioned a rock mechanics study to evaluate key rock properties in the reservoir. However, since the properties measured to predict sanding in the reservoir are common to wellbore stability modeling, the rock data was used to predict the safe drilling window for drilling in the reservoir. Hole collapse and fracture gradient pressures were calculated as functions of hole angle and azimuth for all possible combinations, and potential wellbore instability issues could be determined. The 100% permeable and 100% impermeable cases were also investigated, in order to highlight the effect of the sandstone permeability on changes in the width of the safe drilling window. With little extra cost, using the same data in two different areas (production engineering and drilling) can greatly benefit the operator.
AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery