Predicting well productivity from grain size analysis and logging while drilling

Grain size analysis of drill cuttings and Logging While Drilling (LWD) are used to predict permeability-height (KH) in high-angle wells. In the Sherwood Sandstone reservoir, Wytch Farm Field, permeability is controlled by porosity and grain size. These can be measured using LWD density logs and sieve analysis of cuttings. KH and Productivity Index (PI) are estimated using permeability-bulk density transforms for each grain size class. A PI of 60 ( - 35 / + 120 ) STB/day/psi was predicted for the first extended reach well on Wytch Farm. The initial PI was 100 STB/day/psi. This test result calibrated the model for subsequent wells. The predicted PI of the second well was 42 ( + or - 15 ) STB/day/psi. The initial PI was 40 STB/ day/psi. The KH plot is used to geosteer the well; optimize perforation intervals, and to estimate PI in wells plugged-back for water shut-off.