Slim LWD Spectral Gamma Ray for Both Well Placement and Petrophysical Evaluation of Clastic Reservoirs in Saudi Arabia

Zeghlache, Mohamed Larbi (Saudi Aramco) | Palmer, Richard (Saudi Aramco) | Abdelkader, Alibassiouny (Weatherford)



With the world’s increasing energy demand, it has become more crucial to safely and efficiently maximize recovery from existing assets. In this effort, there are compelling reasons for focusing on clastic reservoirs where horizontal wells are drilled to maximize reservoir contact and drainage area. In this environment, well placement and real-time petrophysical evaluation are the keys to maximizing net-to-gross ratios.

Technology has recently evolved toward the adaptation of a multi-disciplinary approach and integration of real-time answer products to address formation evaluation challenges. To this end, Saudi Aramco has introduced into their lateral operations the slim size LWD spectral gamma ray in combination with the multi-functional logging while drilling (LWD) technology.

By measuring a formation’s three naturally occurring radioactive components: potassium (K), uranium (U), and thorium (Th) in real-time, petrophysicists can identify clay mineral types in addition to the standard evaluation. This information allows for more accurate formation evaluation through reliable optimizing petrophysical modeling of mineral and fluid types and volumes. It also minimizes uncertainty on the volume of shale (Vsh) estimation, which has an impact on the effective porosity calculations.

From real-time 16-bin spectral gamma ray data and X-Y magnetometers to track the detectors azimuthal position, a high resolution image is preferred — over the standard gamma ray — for properly identifying target entry and for optimizing well trajectory in clastic formations where the lithology changes vertically and laterally.

Technology Description and Application:

The Slim LWD Spectral Gamma Ray tool measures total gamma ray of a formation and the three previously noted naturally occurring radioactive components (K, U, Th). This technology is used in slim holes as well as in relatively larger holes with the 6.75” or 4.75” collar sizes. To produce a real-time azimuthal gamma ray image, the tool must be rotated and run with “s” directional sensors. The 6.75” tool has three (3) spectral detectors and the 4.75” with one (1) detector. Each scintillation-based detector is mounted in a pocket on the outside of the collar with a thin protective sleeve over the detectors; thus enabling the highest possible gamma energy to reach the detectors.