Petrophysical Characteristics and Implications on Both Wellbore Strengthening and Wellbore Stability: A Case Study, Balsam Field, Nile Delta, Egypt

Abstract

Abstract Improper drilling fluid formulation still trigger the wellbore stability challenges and the main reason is the incompatibility of drilling fluids with formations characteristics. Thus, it is important to understand the interaction between rock and drilling fluids. This case study represents an approach of utilizing the petrophysics evaluation of both Abu Madi and Qawasim formations in providing an additional tool to understand the drilling challenges root causes and provide a mitigation plan. A petrophysical evaluation constructed for three wells in Balsam field with focus on petrophysical parameters related to both wellbore stability and wellbore strengthening such as shale volume (Vsh), porosity (phi), permeability (k), formation water salinity besides the litho-facies and the clay types and mineralogy. For the same selected wells, both drilling and geomechanics events delineated from both the daily drilling reports (DDR's) and drilling fluids report (DMR's) plotted against the petrophysics log parameters to understand the relationship between formation characteristics and drilling challenges as a part of pre-drill risk assessment considering the petrophysics parameters. Tight spots, pack off and differential sticking were the major drilling challenges through the studied three wells. The study concluded that some of fluid types/chemistry were not adequate to interact with both shale of both Abu Madi and Qawasim formations, moreover the study revealed that the wellbore strengthening package need to be modified. Shale volume (Vsh), clay mineralogy from petrophysics analysis linked with wellbore stability events as a part of risk assessment phase using petrophysical parameters. The same information will help the drilling fluids team to formulate the clay inhibitive recipe of the utilized fluids, optimize the water activity (Aw) using the optimum mud salinity to minimize the pressure transmission and potential time-dependent failures. The other petrophysics parameters such as porosity, permeability and pore throat size utilized for dual functions; the first function was in risk assessment to delineate the troublesome zones that could be related to potential invasion, downhole losses, differential sticking and reservoir damages meanwhile the second function was useful in wellbore strengthening simulation as an input data with other well general information to optimize the wellbore strengthening additives based on reservoir characterization using a specific wellbore strengthening software. Utilizing the petrophysics information can help in both pre-drill risk assessment and for better understanding the mechanisms of subsurface challenges. Moreover, the petrophysical data will adequately assist drilling fluids team to optimize/customize both wellbore stability and wellbore strengthening additives and all related mud parameters to efficiently stabilize the troublesome formations physically and chemically in additions to the mechanical action through exact geomechanics mud window.