Deep EM Method for Proactively Prediction of Resistivity ahead of Bit to Determine Salt Bottom Position

Abstract

Most wells in TOC block A need to be drilled through the salt formation, which is always with troubles, like high-pressure salt water, mud loss, stuck pipe etc. Furthermore, the salt formation has great heterogeneity, thickness and depth of the salt different from well to well. For these wells, it's very important to drill through the salt formation safely then set casing accurately at the bottom of it. The common practice for client is to drill using small bit and then reamer to large hole through the salt formation, which is costing time and large uncertainty in salt formation detecting. The deep EM look-ahead method application aims to help client to predict the bottom of salt formation, then set casing to the right place. This new approached method in this paper based on deep EM technology can detect formation features, especially development for measuring resistivity contrasts ahead of the bit in real time to reduce cost and risk during drilling operations. It provides a step change with regard to precision in detecting changes in resistivity properties ahead of the bit in vertical and low-angle wells. This method can reduce mainly drilling risks and improve landing but detecting potential drilling hazard and reducing depth uncertainty ahead of the bit. The main application of this method in this paper is to detect salt bottom ahead of bit. Using this method, we can now finally drill and react pro-actively on formation resistivity properties several meters ahead of the drill-bit, instead of drilling reactively on resistivities at or behind the bit. After one well application, we successfully helped client detecting the bottom of formation and setting case to the right depth. In this paper, a pilot project case will be discussed detailly featuring successful application of EM method to react pro-actively on formation resistivity changes ahead of bit, helping client reducing drilling risks.