Role of Cement Fluid Loss in Wellbore Completion

Abstract

occurs after cement PIacement. Sufficient delays in the loss of pressure are obtained for an API fluid-The fluid-loss behavior of cement slurries 1oss requirement in the range of 10 to 30 mL/30 min against permeable formations and its relationship to with the actual value dependent upon wel1bore geominterzonal fluid migration have been investigated. etry, overbalante pressure, mud fluid-1oss properties Static fluid-loss testing, designed to simulate cement and cement S1urry design. PIaced in a wal1bore, has shown that the cement fluid-10SS rate through a deposited mud filter cake decreases with time.This decrease in fluid-loss rate INTRODUCTION is dependent upon the designed fluid-1oss properties of the cement S1urry, and significantly influences the During the dril1ing and completion of oil and gas loss of hydrostatic pressure required to control reservoirs, formation fluids are contained by the formation fluids. Once the pressure starts to decay, hydrostatic pressure exerted by the wellbore fluids. formation fluids can potentially enter the wellbore The loss of hydrostatic pressure during drilling causing ineffective zonal isolation and, in some operations can result in well blowouts and "gas kicks" cases, gas migration to the surface. at the surface.1 Hydrostatic pressure loss after wellbore completion also permits the invasion of The mechanism described indicates that hydroformation fluids into the wellbore.2'3 Unlike drilstatic pressure is initially transmitted after cement ling operations, the problem of fluid migration after placement.During this period, fluid loss to the completion is compounded since the cement has been surrounding formation is compensated for by an equal permanently placed in the wellbore. The result may be decrease in slurry volume.The resulting changes in poor zonal isolation, annular pressure buildup, gas the solid-to-water ratio and gelation properties flow to surface and conrnunication with nonproductive coupled with the growth of the cement filter cake or productive zones. cause the pressure against the formation to eventually decrease.The rate of pressure decrease is dependent Several investigators have assumed that the upon the fluid-loss rate and the slurry's compress-hydrostatic pressure loss is due to volumetric changes ibility.Once the pressure approaches the formation associated with cement hydration and fluid loss to pressure, interzonal fluid flow through the cement permeable formations.2-lg Other reported reasons for slurry occurs with its rate initially governed by the fluid flow are poor cement placeinenttechniques,q high cement fluid-loss rate. cement free water [sedimentation], ll cement gellin properties12-16 and excessive thickening times.~9 Several correlations have been made relating

How Fluid Loss Influences Primary Cementing: Literature Review and Methodology

“…The literature has mentioned that cement additives (e.g., lignosulfonate retarders) may induce damage while filtering into the formation. 17,18 The high pH and salt content of cement filtrate also may cause damage. 10,16,19,20 We derive a criterion from the observation that, if the depth of filtrate invasion remains smaller than the perforation length, any formation damage will be bypassed.…”

Why Cement Fluid Loss Additives Are Necessary

“…If we assume that the fluid loss volume v,l is proportional to the filter cake volume 1~, 1~ = RYtt [1], the factor R is then, for a given slurry composition S = V' IV, only depending on the cake porosity, <Pc : 11 R = S-<f>e(l + S).…”

“…Indeed, it is ·generally clearly acknowledged that a lack of fluid loss control may be responsible for primary cementing failures, due to excessive density increase or annulus bridging and that formation invasion by cement filtrate may be deleterious to the production [1,2]. With respect to squeeze-cementing, the problem is to adjust the level of fluid-loss to perforation size and formation nature [3,4].…”

“…Therefore, by comparing thickening time and bridging time, a maximum value for the cement cake permeability can be deduced which is then expressed as an API fluid loss value. 1 References and illustrations at the end of paper 853 From typical mudcake resistances it can be estimated that, both in dynamic and in static conditions, the fluid loss could, in some conditions, have to be reduced to an API value one order of magnitude lower than what is generally considered as a fair control of fluid loss. Some examples are given.…”

Dynamic Filtration of Bentonite Muds Under Different Flow Conditions

“…fluid loss. 4 DYNAMIC FILTRATION OF BENTONITE MUDS UNDER DIFFERENT FLOW CONDITIONS SPE 18038 the experiment. A more detailed presentation of the data can also be given but will be reported elsewhere.…”