Mud Weight Evaluation Based on Safe Mud Window in Drilling Well “X-1” to Overcome Caving and Partial Loss Problems in The Oil Field

Abstract

Drilling of Well X-1 in the North Sumatra Basin at a depth of 2887-3186 m TVD occurred partial loss, and caving at a depth of 500-1650m TVD. To overcome this problem, it is necessary to use the safe mud window concept. Drilling mud density planning must be greater than the pore pressure and shear failure gradient but not more than the minimum horizontal stress and fracture pressure. The purpose of this paper is to make an accurate subsurface pressure analysis and to overcome problems caused by the mud weight planning errors used based on the safe mud window, and can be used as a reference for further drilling of wells that have field conditions and stratigraphy such as the Well X-1. In conducting safe mud window analysis, there are several parameters that need to be estimated in order to make a safe mud window, namely formation pressure, formation fracture pressure, minimum horizontal stress, maximum horizontal stress, vertical stress / overburden pressure, and shear failure gradient. From the results of the safe mud window on Well X-1, the actual mud weight data used during drilling is entered. After being analyzed, at a depth of 500-1050 m TVD caving occurs because the density value used is smaller than the shear failure gradient, while at a depth of 1050-1600m there is kaolinite mineral which causes caving. At a depth of 2829-3281 m TVD the density value is greater than minimum horizontal stress (SHmin). Here, caving occurs if the density value used is smaller than shear failure gradient and partial loss occurs if the density used is greater than SHmin. Based on the safe mud window, the optimal mud weight for drilling at a depth of 36-354.2 meter on a 20” route is 9.2-9.4 ppg. At a depth of 354.2-948 meter on a 16” route is 14.49-15.33ppg. At a depth of 948-1619 meter on a 13 3/8” route is 15.45-17.65ppg. At a depth of 1619-2829 meter on a 9 5/8” route is 17.36-17.76ppg. At a depth of 2829-3281 meter on a 7” route is 16.57-16,7ppg. And at a depth of 3281-3796.1 meter is 13.49-13.74ppg in order to avoid partial loss and caving problems.