Formation Evaluation-While-Drilling Technology Improves Data Delivery

Abstract

Young Technology Showcase Today’s drilling engineering teams are continually looking for better ways to mitigate risk and improve health, safety, and environmental conditions at the rig site. Many operators would prefer to acquire a comprehensive suite of petrophysical measurements while drilling—without incurring the risk and cost associated with deployment of chemical nuclear sources. Traditionally, both wireline and logging-while-drilling (LWD) tools have depended primarily on radioisotopes such as americium-beryllium to generate high-energy neutrons for porosity measurements, and cesium to generate gamma rays for bulk density measurements. However, transportation, storage, handling on the rig floor, and potential abandonment of radioactive sources at the wellsite should the tools become stuck require special safety precautions and costly, time-consuming procedures. In remote geographic regions, mobilizing chemical sources can be slow and logistically complex. If a bottomhole assembly (BHA) with a chemical source becomes stuck, complicated fishing procedures can waste precious rig time, and delay eventual production of oil and gas. To meet the growing industry need for an alternative to radioactive chemical sources, Schlumberger recently released NeoScope sourceless formation evaluation-while-drilling solution (Fig. 1). This technology is unique in three ways. It is the first LWD tool to introduce a completely new nuclear measurement to the industry—sourceless neutron gamma density (SNGD). It is the only tool in the industry that provides formation density and neutron measurements without the need for chemical nuclear sources. Finally, it is the first tool to provide collocated density and neutron measurements (Fig. 2). Development and Field Testing LWD tools have typically used two chemical nuclear sources to obtain neutron porosity and bulk density. In partnership with Japan Oil, Gas, and Metals National Corporation, Schlumberger first developed and deployed a pulsed neutron generator (PNG) for commercial standard neutron porosity, spectroscopy, and sigma measurements 7 years ago, eliminating the need for one of the chemical sources (241AmBe). However, development of SNGD was not yet mature enough for commercial use. The only way to acquire a reliable density measurement was still to use a cesium source. Hence, it remained impossible for operators to obtain a comprehensive sourceless suite of petrophysical data while drilling. Ongoing research and engineering led to modifications of existing technology, design of new detectors, and development of sophisticated characterization algorithms and calibrations to provide the first commercial SNGD measurement—a true breakthrough. Since 2005, extensive laboratory modeling and experimentation, as well as more than 200 field tests in more than 30 countries have been conducted to verify and refine the new SNGD measurement. Tests have been carried out in a wide range of formations under many different environmental conditions. Comparisons of the new PNG-based density measurement with conventional bulk densities derived from chemical sources showed good correlations both in carbonates and sandstone formations, onshore and offshore (Fig. 3). Field testing extended through early 2012, and the commercial solution was officially released in June.