Fractures in the Jurassic Arab Formation and Lower Fadhili Carbonate Member of the Dhruma Formation, Saudi Arabia

A study on the Jurassic Arab Formation and Lower Fadhili carbonate member of the Dhruma Formation, in the north-eastern coastal area of Saudi Arabia, was conducted to understand the nature of the fractures and their potential impact on fluid flow. A total of 50 km of borehole images and cores were used, in addition to well test data and drilling records from 43 key wells. The tectonic discontinuities observed include mesoscopic faults, extension fractures and tectonic stylolites. Fracture clustering occurs in zones of mesofractures (including faults), which crosscut bedding boundaries or cluster around bedding or tectonic stylolites (stylolite fractures). Vertical variation in average fracture density between layers (mechanical stratigraphy) is controlled by rock mechanical properties, which are functions of lithology (limestone versus dolomite), porosity, and texture. The majority of the fractures are steeply dipping stylolite fractures, which are mostly short with heights ≤ 2ft (smaller than the average individual bed thickness). Only a few percent of the fractures are 2 to 4 ft in height. The shortness of the fractures, and the rareness of through-going fracture clusters, diminishes their potential impact on fluid flow to a subtle and localized level of enhancement of flow.