Abstract:
Acid stimulation is one of the primary methods for improving productivity of oil & gas wells. A properly designed and executed acid job can improve production rate & subsequent cash flow. The matrix treatment of carbonate formations with acid works well due to favorable kinetics of carbonate dissolution by the acid. A variety of different acids may be used in treating carbonate formations and the risks of secondary precipitation are minimized. In contrast to carbonate formations, sandstone formations are only susceptible to dissolution by hydrofluoric acid (HF). However, at more extreme mineralogies, temperatures, and reservoir conditions the dissolution reactions in a sandstone matrix may be so rapid that the resulting precipitation reactions are often uncontrollable. To account for this, organic acid/HF blends began to be used in matrix acidizing for retarded dissolution of aluminosilicate. The slower reactions of organic acids allowed greater control over the dissolution kinetics at higher temperatures. An additional means of minimization of precipitation in sandstone acidizing is through the use of multiple, functional stages of fluid in sequence, including a brine preflush to displace incompatible metal ions, followed by an acid preflush to dissolve the calcium carbonate in the matrix. After the removal of the carbonate matrix, hydrofluoric acid is used for the main treatment. In this paper, case history of matrix stimulation of Datta Sand Stone reservoir will be presented. The formation is usually characterized by low porosity and low permeability reservoir and is distributed in Potwar and Kohat basins. First time in Pakistan, Datta formation is stimulated in deep wells in Dakhni Field of North Potwar sub-basin. It is a gas condensate producing formation with liquid yield of about 50 bbl/MMscf. DST analysis showed high skin value while subsequent well test analysis confirmed the initial DST results. Transient analysis indicated that by removing the skin, production can be increased. After well cutting analysis, acid recipe was prepared to treat the subject reservoir. Due to clay distribution in Datta formation, special attention was paid in the preparation of recipe. Stimulation was designed and successfully carried out in two wells. Gas production was increased by 60 to 200 % from the base production while well head flowing pressure was increased from 2000 to 5000 psia. It proves that matrix acidizing is a cost-effective procedure for removing the causes of well impairment in sand stone formations and greatly helps in increasing the productivity of the well.
Page(s):
269-282
DOI:
DOI not available
Published:
Journal: Proceedings SPE-PAPG Annual Technical Conference, Volume: 0, Issue: , Year: 2009