Reductions In the Productivity of Oil And Low Permeability Gas Reservoirs Due to Aqueous Phase Trapping

Abstract

Many hydrocarbon bearing reservoirs exhibit the potential for significant productivity reductions due to adverse relative per-meability effects associated with the retention of invaded aque-ous fluids. Those fluids could include water-based drilling mud filtrates, completion fluids, fracture fluids, workover fluids, kill fluids or stimulation fluids (including spent acid). This paper i entities potential mechanisms behind phase trapping and identifies particular reservoir types which tend to be susceptible o this type of formation damage, most notably low initial wat saturation gas reservoirs and strongly oil-wet oil reservoirs. Laboratory techniques to investigate the severity of aqueous trapping and various remedial techniques are described, and I o field case studies illustrating the potential for permeability impairment due to invasive aqueous trapping are presented. One case study describes a series of wells completed in the Paddy fo ation and the second in the Cadomin formation in the Deep Basin area of central Alberta (both gas producing zones). Laboratory case studies documenting the phenomenon of aqueous phase trapping in strongly oil-wet porous media are also presented. IntroductionOil and gas bearing formations are potentiallv susceptible to many different types of formation daiiiage(I 6). In this paper we are exclusively concerned with damage associated with aqueous phase trapping (or water trapping or blocking as it is often referred to). To understand the concept of aqueous phase trappin , it is essential to differentiate between the concept of initiat (often referred to as connate) aqueous phase saturation (S,i) and irre-ducible aqueous phase saturation a) Initial aqueous phase saturation is the initial average frac-tional portion of the pore space which is occupied by watei-. The value of the initial aqueous phase saturation is con-trolled by numerous factors, includina reservoir geology, depositional history, temperature, wettability, height above free water contact and pore size distribution. The key point to differentiate in this area is that the initial aqueous phase saturation is not necessarily, and often is not, equal to the irreducible aqueous phase saturation and can be either higher or lower than the irreducible saturation. It is in the secoii(i case, where the S,i is less than S,i,.,., where productivity November 1994, Volume 33, No. 9 k. k, i@Kiw -0 85 0 8 _ ia 0 6 > 0 4 Ig @SM,, -0 85 0 2 k. ., kg = 0 03 I,,@d..ibl. S. 10%@ (,5%) 65% S@, 00 0 0 0 2 0,4 0 6 0.8 Water Saturation FL(,URE 1: Mechanism of aqueous phase trapping. reductions due to phase trapping can occur. h ) Irreducible aqueous saturation represents that saturation which is forced to exist in the reservoir by capillary mechan-ics. Once again, the value of the Swi, is determined by para-meters such as the reservoir morphology, pore size distribu-tion, poi,e throat size distribution, wettability, surface rough-ness, etc. We often obtain estimates of Swi, through the use of air-brine or air-mercury capillary pressure tests. ...

Water And Hydrocarbon Phase Trapping In Porous Media-Diagnosis, Prevention And Treatment

“…Bennion et al (1994) (1) have provided a detailed discussion of the basic mechanisms of aqueous and hydrocarbon phase trapping and associated reductions in permeability. Aqueous phase trapping can occur in both oil and gas reservoirs and may be associated with reservoir situations where the reservoir exhibits a sub-irreducible initial water saturation.…”

The Application of Fractal Dimension on Capillary Pressure Curve to Evaluate the Tight Sandstone

“…Bennion et al (1994) have also provided a detailed discussion of the mechanisms of aqueous phase trapping. Penny et al (1983) pointed out that the capillary pressure, wettability and relative permeability are controlling the load water recovery following hydraulic fracturing treatments (Wang 2017).…”

Wellbore instability in shale gas wells drilled by oil-based fluids

“…Water, white oil and kerosene invaded into formation are subject to be adsorbed on the surface of pores or natural fractures to induce water or oil phase trapping [21,22]; because of the high capillary pressure phase trapping damages is always fatal to tight gas reservoirs and difficult to be removed. Unfortunately, oil phase trapping induced by white oil and kerosene may be more fatal than water phase trapping because white oil or kerosene is prone to be adsorbed by organic matter of shale, the main place storing adsorbed shale gas.…”