Abstract
Abstract
The number of maturing reservoirs is increasing and the need to manage water production is becoming ever more pressing. As has been observed repeatedly it requires at least the same amount of energy to produce a barrel of water as it does to recover a barrel of oil. Water Shutoff Chemical Systems, especially the new generation of Relative Permeability Modifiers (RPM), offer a potential solution to the problems of excessive water production.
Polymers, in the form of weak solutions, are intended to control water production, especially when oil bearing and water zones cannot be isolated. These products, identified as Relative Permeability Modifiers, are introduced to the reservoir, typically by bullhead injection or as fracture additives, with the intention of reducing the relative permeability to water, while avoiding as much as possible any reduction in the relative permeability to oil. The phenomenon that the placement seeks to induce is disproportionate permeability reduction (DPR) and will, where successfully applied, significantly reduce production costs.
The claims made for the various RPM products in the technical and sales literature suggest that their applicability is essentially universal; being largely independent of such key parameters as wettability, pore throat size, clay content, saturation profile and temperature. If this were the case, RPMs would be employed on a routine basis, rather than infrequently, accompanied with a healthy level of scepticism. In reality each RPM treatment should be case specific, affording the client the opportunity to test the various products on offer. It also provides the suppliers with the opportunity to optimise the formulation of their particular Relative Permeability Modifier through the offices of an independent laboratory.
This screening process is achieved through the deployment of representative and fully characterised core material, prepared to preserve factors such as wettability and clay fraction integrity. The testing on this material, undertaken at reservoir conditions of temperature and pressure, yields, on a "before and after" treatment basis, effective permeability and saturation data sets. From these values (Residual) Resistance Factors for the two fluid phases are produced, to quantify the effectiveness of the impedance of water flow, without significantly reducing oil production.
Introduction
Relative Permeability Modifiers (RPMs), after a period of extreme user scepticism, are once again being considered as an effective method of controlling unwanted water production in both oil and gas reservoirs. The inclusion of RPMs in the conformance engineer's portfolio of possible remedial solutions is being driven, in part, by the introduction of new and improved products by a number of major chemical suppliers. Principal amongst these offerings are the RPMs from Halliburton (WaterWeb, CW-Frac), BJ Services (AquaCon) and Clariant (RelTreat). These companies are responding to the ever growing number of maturing fields, which are plagued by excessive water production and to the demands of clients to extend viable hydrocarbon output beyond current predictions.
The RPM's original fall from grace was driven by extravagant claims for universal applicability, in essentially all lithologies. The point has been made that if the majority of RPM treatments had met with measurable and general success, their deployment would not have declined quite so dramatically (1). It may be argued that this pattern of initial misplaced optimism, followed by a broad rejection of the products and the techniques, could ensnare the present range of products, thereby dissipating their believed potential.