Prediction of optimum wellbore trajectory by minimizing sand production
Nadarajan, Bob H.
Engineering Honours Degree 2008
University of Adelaide
Sand production is a major problem in almost all oil and gas sandstone reservoirs. Disintegrated sand grains caused by unconsolidated formation or wellbore failure are the main sources of sand production. Due to its adverse effects on productivity, equipments, facilities as well as health and environment, operators have been spending billions of dollars annually to mitigate the problem associated with sand production. Therefore, Sand Management Strategy is introduced to address issues related to sand production.
Sand Management Strategy suggests that the risk of sand production can be minimized by operating below a certain drawdown pressure, above which sand production will occur. The certain limiting value is termed Critical Drawdown Pressure (CDP). This concept is coupled with drilling strategy through wellbore trajectory optimization which locates the most stable orientation with respect to the relative magnitude of in-situ stresses to construct a sand production prediction model.
Thus, in this paper, a sand production prediction model is presented to predict the optimum wellbore trajectory that maximizes drawdown pressure for which the risk of sand production would be minimal. It proposes optimum wellbore trajectory based on the highest CDP that could be achieved by any combination of wellbore inclination and wellbore azimuth for a given set of input parameters; in-situ stresses, rock properties and reservoir pressure.
Several sample case studies and sensitivity analyses are carried out using the proposed model to compute for the optimum wellbore trajectory for different fault regimes. The results have demonstrated that for a given set of input parameters, there will be an optimum wellbore trajectory that could deliver highest drawdown pressure with minimal risk of sand production. A generalized optimum wellbore trajectory for reverse, strike-slip and normal fault regimes is proposed respectively. For horizontal well, a generalized optimum wellbore orientation with respect to minimum horizontal stress direction has also been established for different fault regimes.
This paper, especially the proposed sand production prediction model, will be a useful guideline for engineer to minimize the risk of sand production by optimizing wellbore trajectory.