Successful Application of New LWD Platform Provides Integrated Real-Time Formation Evaluation in the Mediterranean Reservoirs

Abstract

As the global power scenario changes with increased demand for oil and gas, remote and challenging (deepwater offshore, high pressure-high temperature, high-angle wells) locations are drilled in an ever-demanding exploration effort with minimum or no experience in the area. To meet the demand and associated financial implications, operators are drilling high-angle wells that require special care from well stability, completion, and formation evaluation, to name a few. Complex reservoirs require complex trajectory and therefore proper well placement. To place a well accurately, the evaluation of acquired data requires real-time interpretation. In Egypt, Petrobel is following the trend and has been drilling deviated wells to enhance production in the Mediterranean by using a new logging while drilling (LWD) platform for formation evaluation. The data delivered by this service includes not only traditional measurements such as resistivity, density, neutron porosity, gamma ray, and caliper, but also induced spectroscopy and sigma. The sigma measurement is used for saturation evaluation independent of resistivity. The availability of two independent saturation estimations provides additional confidence. Spectroscopy provides formation mineralogy and accurate clay fraction, which enhances shaly sand interpretation. Formation evaluation in real time provides accurate estimates of hydrocarbon in place and allows for comprehensive decision making. The field is approximately 70 km from the coast of Alexandria, Egypt. The main reservoir is predominantly sandstone with gas and condensate. Highlighted in this study:Real time interpretation based on capture spectroscopy and sigma combined with the traditional measurements.Lithologic and mineralogic evaluation using capture gamma-ray spectroscopy measurements on LWD in real time.Independent gas saturation estimates from both resistivity and sigma measurements on LWD in real time.Real time formation evaluation requires minimum inputs from user, making it a powerful tool for operators in the decision making process. Introduction The new LWD platform is a substantial improvement over the previous versions of LWD tools that were much longer than the current version where one single collar 26 ft long tool combines both drilling and formation evaluation measurements (Figure 1). Measurements include resistivity, density, porosity, gamma ray, dual caliper and two new measurements to the LWD world which are elemental capture spectroscopy measurements that provides detailed lithology information in real time and formation capture cross section (sigma)1 providing an alternative to resistivity for fluid saturation calculation in saline formations in real time. The tool also can be run without chemical sources where the density measurement is derived from the interaction from neutrons with the formation which are generated from the pulsed neutron generator (PNG, also known as minitron) which is an electronic source of generating neutrons. The tool, therefore, could be run with no chemical sources or with only the cesium source. The AmBe chemical source for neutrons has been replaced by the electronic source PNG. The dual ultrasonic caliper 180 degrees apart permits borehole caliper measurement even when sliding and provides high resolution caliper measurement at 16 different azimuths while rotating.