A Method for Calculating More Accurate Stratigraphic Positioning of Horizontal Wells Using Continuous Inclination and Azimuthal Gamma Ray Images Even While Sliding

Abstract

Geosteering long lateral wells in narrow target windows demands accurate stratigraphic positioning, true vertical depth (TVD) positioning, and apparent dip determinations. Using positive displacement motors with alternating slide and rotate drilling modes to control the well trajectory, along with standard 90-ft surveys and single-detector azimuthal gamma ray (GR) tools, have proven to be inadequate. To overcome these issues, a new method has been developed that combines continuous measurements and uses a four-detector azimuthal GR tool. The bottomhole assembly (BHA) used here is equipped with two inclinometer packages and a four-detector azimuthal GR logging-while-drilling (LWD) tool. A high-resolution survey is calculated using a combination of the two continuous inclination survey data sets for the deeper portion of the well and the stationary survey data from the shallow (low inclination) portion of the well, which provides a more accurate well path that better reflects the TVD positioning of the wellbore. The four-detector azimuthal GR tool is used to generate high-quality wellbore images, both while sliding and rotating. This enables more accurate structural dip angles to be determined from the continuous GR images. It also leads to better stratigraphic and structural positioning of the wellbore and a better understanding of changes in stratigraphy across the length the lateral section. Combining more accurate surveys with complete GR images and more accurate dip picking enables a better determination of the stratigraphic position of the wellbore and its path through stratigraphic layers. The wellbore can be divided into various up- and down-drilled sections that can be compared side-by-side using true vertical thickness (TVT) methods to show lateral continuity of the beds.