Refracturing in Old, Mature and Depleted Carbonate Reservoirs in Saudi Arabia for Production Enhancement

High temperature, low reservoir pressure, high permeability contrast, high H2S content, long perforated interval, production decline, existing hydraulically induced fractures, FeS scale, and mature and aging completions are some of the tough challenges encountered in certain carbonate reservoirs in Saudi Arabia. These wells require periodic mechanical descaling operations using coiled tubing. The reservoir suffers tremendous damage during the descaling process and requires restimulation to restore and/or enhance production. The damage is noticed to be higher in non-monobore completion. High rate matrix acid stimulation treatment has been often found not effective to restore and/or enhance production. Acid re-fracture treatment is required to bypass damage and achieve effective new etched fracture length, but the aging completion often disqualifies the well to be a candidate for refracturing treatment. The wells discussed in this paper have been acid fractured in the past and produce for over 20 years with significant production decline. The wells were isolated by pumping large volume of calcium carbonate (CaCO3) chips into the formation prior to the descaling operations. During the descaling of 4.5 in. tubing and 7 in. liner completion, additional near wellbore damage is unintentionally introduced into the formation from the precipitation and broken scale buildup from the wall of the 7 in. liner. Subsequently, acid refracture treatment was effectively placed allowing better and new stimulated rock volume in the depleted formation bypassing the induced near wellbore damaged. The post stimulation flowback analysis showed an improved productivity from mature and depleted reservoirs after the refracturing treatments. This paper focuses on the challenges of refracturing old, mature and depleted carbonate reservoirs, well candidate selection, and treatment design, execution and evaluation.