How to Apply a Blocking Gel System for Bullhead Selective Water Shutoff: from Laboratory to Field

Abstract

This paper describes a new method for water control by the use of bullhead injection. A water based gelant is emulsified in oil and injected into the formation. The emulsion is designed to separate into a water phase and an oil phase at static conditions in the formation. Upon reaction in the formation the water phase gels up while the oil phase remains mobile. It has been found that the controlling parameter for disproportionate permeability reduction (DPR) is to control the fraction of gel occupying the porous media. The water fraction in the emulsion controls the reduction in relative oil and water permeabilities. A program was undertaken to verify this DPR method in a field test, using a commercial blocking gel system. The first treatment was performed in well 30/3 A 16 T2 at the Statoil operated Veslefrikk field offshore Norway. Results show that water production was reduced by 30% after the pilot test, while maintaining the oil rate. As expected, total well productivity was reduced by more than 80%. The treatment consisted of 124 m3 emulsion, bullheaded from surface. Step rate testing and ion water analysis were combined to study the relative change in flow contribution between the 6 perforated intervals. Introduction The increasing number of high water-cut producing wells requires simple and cost effective water control technologies. One option is bullhead injection of chemicals capable of reducing the water permeability more than the oil permeability, normally described as Disproportionate Permeability Reduction (DPR) or Relative Permeability Modification (RPM). DPR will be effective in multilayered reservoirs without crossflow and with some zones producing clean oil or in treating coning problems.[1–3] In such situations DPR treatment will reduce the water cut and may result in increased oil production. The existence of DPR fluids is well known.[4–8] DPR fluids may be classified as polymer systems, weakly crosslinked gel systems or rigid gel systems. The polymer systems are the most frequently used. The DPR mechanism has been explained by polymer adsorption on a water-wet rock surface.[9,10] This will reduce the effective pore space for flowing water. The ratio between the thickness of the adsorbed layer, e, and the pore radius, r, is used to express the permeability reduction, RRF (defined as the ratio between permeability before and after treatment), using Poiseuille flow in a bundle of capillary tubes. ………………………………………..(1) The oil will flow more or less un-restricted in the middle of the pores. Consequently the oil permeability reduction, RRFo, will be lower than the water permeability reduction, RRFw. From Eq. 1 the following can easily be derived:RRF will decrease with increasing pore radius, i.e. increasing the permeability.RRF will increase by increasing the thickness of the adsorbed layer. The latter one can be obtained by using polymers with larger molecular weight and higher affinity for adsorption. Alternatively weak gels or aggregates can be formed in-situ by injection of polymer and crosslinker.[5,11–12] Often, the polymer and the weakly crosslinked gel systems involve additional retention mechanisms, such as pore trapping. The use of preformed gel particles will also increase the effective adsorption thickness.[13] Rigid crosslinked gel is normally used for total blocking. Blocking gels have DPR properties[7,14–17] but for practical purposes in matrix treatment the oil permeability reduction has been recognized far too high for bullheading. However, crosslinked gels could be promising alternatives if the permeability reduction, RRF, can be controlled. This is mainly because crosslinked gels show (i) better temperature stability, (ii) DPR properties regardless of wettability and (iii) high RRF also in high permeability zones. A crosslinked gel will probably also be more resistant towards the high shear rates close to the wellbore. Consequently the volume of active DPR fluid can be reduced. It has been demonstrated that RRF depends on the fraction of gel occupying the pore space.[15–16,18]

Influence of Surfactant Structure on the Stability of Water-in-Oil Emulsions under High-Temperature High-Salinity Conditions

“…Furthermore, emulsification technology has been extensively applied in the oilfields [7][8][9][10]. Usually, the emulsion contains two or more partially or completely immiscible liquids [11], where the dispersed phase exists as droplets suspended in the continuous phase.…”

“…Also, it is used in well productivity enhancement via asphaltene deposition removal [21] drag reduction in multiphase flow [10] and for the control of excessive water production [8,22]. Emulsification technique was introduced in the oil industry through the use of emulsified acids in 1933.…”

“…In a patent, Stavland and Nilsson suggested an injection of the gelant (crosslinked polymer) as an emulsion for RPM field application [22]. In work by Stavland et al [8], an aqueous polymer gelant is emulsified into an oil and then injected as one component. Eventually, the solution separates into an oil phase and water phase upon reaching the reservoir.…”

“…Eventually, the solution separates into an oil phase and water phase upon reaching the reservoir. Afterward, the water phase gels up in a water-wet pathway of a pore space to reduce permeability to formation brine, and the oil phase remains mobile to secure a path for hydrocarbons to flow [8,22]. The control of the gel fraction that occupies the porous media leads to the control of RPM, that is, the reduction in relative permeability of the hydrocarbons and formation brine; this is controlled by the water fraction in the emulsion [8].…”

Applied Technologies and Prospects of Conformance Control Treatments in China

“…Therefore, this product was not used very often. Gels are widely studied for their properties to selectively shut off water and applied in many other countries; however, they are not applied very much in China because of their low success rate [31][32][33][34][35][36][37][38]. A successful technology for selective water shutoff is using O/W emulsions by bullhead injection, which was reported to selectively control water production for more than 500 production wells in China [39,40].…”