Sustained Gas Production From Acid Fracture Treatments in the Khuff Carbonates, Saudi Arabia: Will Proppant Fracturing Make Rates Better? Field Example and Analysis

Abstract

Abstract Acid fracture treatments in the carbonates are widely applied to enhance well productivity. Some laboratory experiments conducted on actual core specimens under in-situ conditions illustrate that the etched conductivity can reduce with time and eventually close the fracture. In some 100+ wells that have been fractured thus far in the Saudi Arabian Khuff gas reservoirs, long-term sustainability of fracture lengths and conductivity has been demonstrated through fracture and production diagnostics. The phenomena of fracture closure observed in the laboratory studies on certain cores may not therefore be generalized to represent all reservoirs and fields. Nevertheless, longer fracture lengths than generally achievable by acid fracturing are often desirable, particularly in gas condensate fields. Proppant fracturing can create longer fractures and has potential for application in such fields. This paper provides field cases and evaluates fracture effectiveness from treatment pressure, pressure transient tests, and production data. Initial computation of fracture properties using measured data during treatment and production transients combined with analysis of pressure transient tests performed later during the production life indicate continued presence of induced fracture. Assessment of fracture operations, reservoir flow characteristics, and mechanical properties suggests that the high rate, high volume acid treatments, and formation heterogeneity in terms of layering and permeability variation which helps in uneven acid etching and thus enabling wormholes to stay open contribute to the long-term sustainability of fracture conductivity, half-length, and well performance. The paper evaluates these parameters and provides an assessment on acid fracturing. Condensate accumulation is occurring in the Khuff reservoirs and this is affecting production rates. Several typical wells are examined to illustrate this point. Liquid dropout is unpreventable, but its effects can be reduced or postponed with longer fractures. Thus the need for proppant fracturing is evident. Saudi Aramco has started testing the viability of proppant fracturing in the Khuff carbonates. The results obtained so far indicate that careful candidate selection and treatment design are needed to guarantee fracturing success. The selection criteria, treatment design and results of Saudi Aramco's first ever proppant fracturing in a Khuff reservoir are examined in this paper.