Selective Water Shutoff Technology Study and Application of W/O Emulsions
Authors: Bai B. , Han M. , Li Y. , Wei M. , Gao Y. , Coste J-P. 
Published: December 2007

Abstract
How to control water-cut of mature oilfields is always a challenging task for field operators. In order to control excess water production, a new selective water plugging agent was developed. It is made up of crude oil and emulsifier. Squeezed into water zones, it forms emulsion when contacting with water. The viscosity of emulsion is 20 times that of the crude oil used, leading to the plugging of the zone. In contrast, when entering oil zones it dissolves into oil without causing any damage. Due to its selectivity, it can be injected into high water-cut production wells by bullhead method.
The purpose of this paper is first to introduce a new emulsifier, then to present the experimental study concerning crude oil emulsions and field operations performed using this technique. The morphological changes of the activated crude oil induced by the mixing with water, the viscous properties of several emulsions and the selection of crude oil are discussed. Coreflood experiments were also carried out to demonstrate the selective placement of the activated crude oil. A formula based on the critical pressure of the emulsions is given to optimize the volume of emulsions to be injected in oilfield experiments.
From Jan.91 to Jun. 99, 238 water shutoff operations using this new technique were performed in Liaohe oil field of CNPC, resulting in 167,000 t of incremental oil and 295,000m3 of reduced water.

Introduction
Excess production water is a very serious problem during waterflooding of heterogeneous reservoir formations. To solve the problem, many kinds of plugging agents have been developed1–3. These plugging agents include: cements, gels, particulates, microorganisms and so on. All these agents were widely used in Chinese oilfields 4.
A key factor influencing water plugging success rate is whether the plugging agent will only reduce water production without damaging less-permeable, oil-productive zones5–8. Four types of treatments have been studied to reduce the damage caused by the plugging agents on non-target zones9–12.Zone isolation: one entire isolated zone is being abandoned in order to allow production from other zones.Dual injection: the treatment is often used in a single, discrete, reservoir zone, when mechanical wellbore control of fluid placement is impossible.Injection of a relative permeability modifier: A relative permeability modifier is bullheaded into all perforated zones. This treatment is often used in these wells in which we cannot identify the specific water producing zone or there may be no barriers beyond the near wellbore region to provide fluid control.Injection of a selective entrance plugging agent: the agent perferentially enter high-permeability high watered-out zones, while it forms face plugging in low-permeability zones. After plugging agent injection, a small volume of dissolver is injected to dissolve face plugging material.
Treatments with zone isolation cannot damage low-permeability zone. However, it has a limited range of applicability, due to the poor distinction between water-producing and oil-producing layers in great majority of the wells, especially in mature oilfields in China. Other types of treatments can damage low-permeability zones more or less.