First Cross-Dipole Shear Wave Imaging Application for Intersecting a Mother Open-Hole from a Near-Parallel Side-Track Wellbore

Abstract

An injector well drilled from an artificial island in UAE left a non-magnetic fish during well control operations across lower Cretaceous reservoirs below the 9⅝-in. casing shoe, exposing all upper Jurassic reservoirs flow units. The situation was a serious concern to field developing and reservoir integrity as aquifer, gas and many layers of oil reservoirs were connected through the borehole below the fish. It was decided to sidetrack around the fish to intersect the original 8½-in. open-hole section. The sidetrack was accomplished, but the first attempt to intersect the mother hole was unsuccessful. Therefore, an innovative solution was needed for detecting the mother hole to intersect it. A combination of cross-dipole deep shear acoustic, high-resolution induction and orientation wireline measurements were advised. These measurements would be used to update the wellbore survey and to detect acoustic reflections from the mother hole for identifying its relative orientation with respect to the sidetrack hole. Detailed measurement-while-drilling (MWD) wellbore survey analyses were conducted for the original and sidetrack holes beside typical corrections, such as Sag and drillstring interference. The deep shear wave imaging data recorded in the side-track hole was processed at multiple X-dipole polarization directions to detect shear reflection from the mother-hole and back calculate its relative position. The high-resolution induction data could not detect the fish from the sidetrack, but few dipole reflections of the mother hole were detected in two locations. The orientation of the reflectors was consistent with the revised wellbore survey analysis, and this information was used to make the directional drilling corrections required to intersect the mother hole. The use of deep shear wave imaging data to identify a nearby open hole was a non-conventional application of this technology, but it definitely facilitated directional drilling operations to successfully intersect a mother hole that cannot be left uncompleted. After the openhole intersection, a good borehole condition was encountered due to the non-damaging fluid system, allowing the well to be completed as per original plan. Achieving this challenging directional drilling objective was critical for the field development plan of these offshore UAE reservoirs. This case study represents the first documented field experience of using deep shear wave imaging data in the petroleum industry for assisting directional drillers to intersect an open hole mother wellbore after sidetracking a fish.