Good Engineering Practices Achieve a 30-Fold Increase in Injection Rates in Selected Niger Delta Reservoirs

Abstract

Abstract Key points of the successful implementation of a pressure maintenance scheme by water flooding in a major operator in Nigeria are presented. The wells considered were completed in July / August 2001 and immediately put on stream. They were designed to dump circa 7,500 BW/D from the sands at ±6100 feet TVD to an aquifer nearby. An initial dump rate as low as 200 BW/D (average) at a maximum surface injection pressure of 1000 psi was recorded prior to the jobs. This was attributed to severe impairment from the pseudo-oilbased mud, incompletely removed with stimulation treatments following perforation. Low permeability or wellbore damage associated with the mud in the drilling phase may also have been responsible for limiting injection rates into these sands, especially if the perforation tunnels during completion, did not extend past the area of mud invasion. The stimulation treatments used a xylene solvent pre-flush and a new HF acid treatment to remove the pseudo-oil and perforation debris damage, improving injection rates significantly. The more than 30-fold injectivity improvements that resulted may have been due to one or a combination of the following:A nitrified acid-aromatic pickle performed before pumping treatment fluid into formation.Pickle volume kept at approximately 25% tubing volumeTreatment performed in segments reciprocation across the perforationsInjection lines flushed to more than expected injection rates to ensure clean injection water.Circulation of tubing to clean water using foamed nitrified fluids during the pickle, helped to bring the spent pickle acid back to surface. Remedial work to further improve the dump rate (and oil sweep) may only be considered if BHP surveys at a future date from closed in wells do not indicate reservoir pressure stabilization or an improvement over the decline previously observed. Introduction The KKK field is an areally extensive field located in a Swamp location in Niger Delta. The field was discovered by KKK-1 well in 1996 and completed in August 2000 as a dual string water injection well in two (2) major aquifer sands (upper and lower reservoirs), one on each (short and long) string. Following this, several other wells have been completed to develop the field. A reservoir study was conducted for the upper and lower reservoir sands to investigate the need for pressure maintenance and artificial lift to maximize oil recovery from the reservoir. This study, supported by the geological interpretation of limited aquifer extent, showed that pressure maintenance by means of peripheral water injection was required to maximize oil recovery efficiency. The water injection wells were therefore needed to restore reservoir pressure so that oil recovery is maximised and GORs are reduced.