Abstract

The objective of the analytical simulator presented here is to predict theopposite and complex effects induced by the injected produced water temperatureand formation damage on thermally fractured wells. The deposition of solidparticles and oil droplets in a fracture and its effect on the InjectivityIndex evolution of an injector is then simulated. The principle is to injectcooled waters like sea water for example during a certain period of time toenable the well to develop a thermal fracture. When the fracture is wellestablished, the re-injection of hot produced waters starts. The model takesinto account the effect of this new water temperature on the viscous flow andon the fracture shrinkage and closure. In the same time oil droplets and solidparticles contained in produced water cause the damage of the reservoir. Thistends to open and propagate the fracture under bottom pressure increase. In thesimulator, the internal formation damage and the external filter cakedeposition in the fracture occur simultaneously. Two internal formation damagedeposition models are taken into account. In a first model the internal damageis supposed to be linear and occurring from the fracture faces to thereservoir. In a second model, despite the growth of the fracture, the internaldamage is supposed to be radial and occurring from the wall of the well to thereservoir. Also, two exeternal filter cake deposition models are considered:the filter cake deposits only at the fracture tip or on fracture faces.Theoretical field cases were considered in the simulations. The differentinternal formation damage and filter cake models were combined together toreproduce the injectivity index evolution observed on real fileds. The examplepresented are chosen to show that, contrarily to common thinkings, the IIevolution can be dominated, in certain circumstances, by the internal damagerather then by the external filter cake deposition. With the present choice ofdata, the II evolution which matches better the commonly observed fieldreponses is obtained when the internal damage occurs in radial flow whateverthe model deposition of the external filter cake is.

Introduction

Today produced water management would be assessed as part of the integratedreservoir management and considered as strategic to the sustainable oilfielddevelopment[1]. Regarding the increasing amount of produced water in maturefields, their re-injection in reservoir becomes very attractive because of themore and more constraining environmental regulations and the increasingtreatment coasts. The re-injection of produced waters is the often a goodenvironmental and economical option because it offers an alternative forconventional pressure maintenance, water flooding or disposal schemes. Todefine the feasibility of produced water re-injection, simulator tools arenecessary even from the early stage of the oil and gas field developmentstudies. According to laboratory experiments[2,3,4] and field[5] observations, the combined effect caused by solid particles and oil droplets contained inproduced waters can generate a severe damage of the formation. In the matrixflow injection regime, because of the small surface exposed by perforations tothe flow and this severe damage, the injectivity of the well decreases quicklyand drastically. The re-injection of produced waters in matrix flow istherefore not a good option, even in high permeability formations at least forthe high flowrates needed to make the injection operations economicallyprofitable. Consequently the re-injection in fracturing regime is the onlyoption allowing to sustain an injection rate and to make the injectionoperations economically profitable. With a fracture, it might be possible tore-inject more "dirty waters" while maintaining a good and acceptableinjectivity and therefore to reduce the size of water treatment installationsat surface. In this case it is important to be able to evaluate the growth ofthe fracture sizes and volumes and to verify if they can accommodate for theamount of particles injected. In this domain analytical[6] and numerical[7,8,9]simulators, coupling fracture growth and damage, were presented in theliterature. They enable to predict the fracture behaviour and injectivityevolution for fractured wells.

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