This paper was selected for presentation by an SPE Progtam Co",mtnee follow.ng review of informalion conlatned in an abstract submitted by .he authOl(s). Contents of the p_r. as presented, have not been rev;ewed by the Societ}f of Petroleum Engineers ana are subject 10 correcllon by the a;Jt!10r(s) The material. as presented. does not necessarily reflect any position of the Society of Pelroleum Engineers. its officers. or members. papers presented at SPE meetmgs are subject to publication rev!ew by Editorial Comml"~ of the Society of Petro/81Jr11 Engineers. P&rmlssron to copy is restricted to an abstract of not "ore than 300 words, Illustrations rnay nol be copied, The ab~ract should contain conspicuous acknowledgment of where and by Whom the paper is pre.ented. Write Libra'ian. SPE. P.O. Box 833835. Rtchardson. TX 75083-3838. U.S.A .. Telex 163245 SPEUT.
This paper shows how rock strength analysis can be utilized in preventing wellbore collapse and sand control problems during production of directional wells. From this study it is seen that selecting the correct production rate can avoid wellbore collapse which cause sand production. When the production rate is increased the reservoir drawdown near the wellbore cause an increase in the effective wellbore wall rock stresses. Using the von Mises rock failure criteria for wellbore stability analysis, the maximum production rate without formation collapse and sand production can be estimated. The parameters that effect the rock stresses at the borehole wall are the in-situ stresses, wellbore inclination and direction, and fluid pressure in the rock which is a function of the production rate. If the decrease in the near wellbore fluid pressure due to high production rate causes the effective stresses to exceed the failure criteria the wellbore will collapse to a certain new diameter. After the new diameter is estimated the volume of produced sand is calculated. The study concludes that possible sand production should be carefully analyzed in all directional wells. The wellbore sand production is a much more severe problem in directional wells and might limit the production rate. The maximum production rates with no sand production can be obtained using the approach in this paper. Introduction Wellbore stability is extremely important for the success in drilling and production. Wellbore instability during drilling may cause stuck pipe, cementing problem, or drilling fluid loss which may cause in a blow out. Wellbore collapse occurs because of insufficient mud. Fig. 1 shows the types of collapse in the wellbore. P. 377
During matrix acidizing stimulation jobs, the use of more acid does not mean more skin reduction during the treatment. The excessive acid volume serves only to dissolve and weaken the matrix rather than remove the damage. The optimum amount of acid needs to be determined in each matrix stimulation case. This is done by calculating the real time skin value which is used to estimate the optimum volume needed. The acid volume and type used in matrix acidizing stimulation is usually based on the experience of the operator in the field. Trial-and-error or on-site injectivity measurements are used to optimize the acid volume. In order to limit trial-and-error exercises, a real-time on-site treatment evaluation method has been developed to assist the field engineer with a new real-time matrix volume estimation technique. History matching and curve fitting the early stages of the acidizing job, the method determines when the maximum damage removal is obtained and corresponding acid volume. This work proposes the use of real-time matrix acidizing data in conjunction with real-time skin effect calculations to estimate the optimum acid volume to be used on-site. The results are compared with three acidizing field cases in the paper, but has been verified for sixteen (16) field cases. The method can be used for optimizing acid volume during matrix stimulation in progress and deciding when to stop pumping the acid. Introduction The concept of skin effect has been used as a magnitude of near wellbore flow impairment. The total skin effect is a multi-component quantity including mechanical skin effects such as mud solid and filtrate invasion during drilling and cementing, formation debris during perforation, and fine migration during production. Actually, the skin effect accounts for any deviation from an ideal undamaged, open-hole, vertical well. "Damage" may be caused by a number of phenomena on which traditional acidizing has no effect. Some of these pseudo-damage phenomena are gravel-pack and partial perforation and penetration. Matrix acidizing stimulation is a treatment intended to remove near-wellbore damage. The determination whether to and how much to stimulate a well and the type of acid treatment should depend on comprehensive pre, real-time, and/or post analysis with high emphasis on quality data gathering. Matrix acidizing job effectiveness can be assessed through real-time or post treatment evaluation of data collected during the acid treatment. During the matrix acidizing treatment, fluids are injected into the well, causing a pressure response recorded at the wellhead. P. 381
SPE Members Abstract This paper addresses the comparison and selection of failure criteria for in-situ rocks in borehole stability analysis. Five commonly used criteria are compared with field cases for mud weight design. The result of case studies indicates that the Mohr-Coulomb criterion, Inner Drucker-Prager criterion and Middle Drucker-Prager criterion are overly conservative, and that the Outer Drucker-Prager criterion is underestimating for designing wellbore pressure to control borehole collapse. It is concluded that the von Mises criterion is more reliable than other failure criteria and should be used for borehole collapse analysis and mud weight design. Based on triaxial test data, this paper also provides failure diagrams for some reservoir rocks. These diagrams can be used as references for borehole stability analysis when similar rocks are encountered in petroleum drilling. Introduction Borehole collapse during drilling and production has long been a problem which results in substantial expenditure to the petroleum industry. Compressive failure analysis is frequently proposed to predict borehole collapse, and consequently, the wellbore pressure required to prevent hole collapse. However, it is unclear to petroleum engineers as which failure criterion should be used in the analysis. Mogi reported that the effect of confining pressure on the fracture strength of rocks follows closely the Coulomb criterion. However, from results of the triaxial compression tests in which all three principal stresses are different, the intermediate principal stress has an important influence, so that fracture criteria, such as Coulomb, Mohr or Griffith, are not entirely applicable. Mogi claimed that the observed behavior under combined stress is adequately described by a failure criterion, which has a form of generalized von Mises criterion. Bradley used the von Mises failure criterion for analysis of collapse of inclined boreholes. Aadoy and Chenevert found that bore hole collapse is caused mainly by shear but also, in some cases, by tensile failure. They utilized the von Mises yield condition for shear failure analysis, and they claim that when the wellbore pressure is equal to or less than the formation pressure, a possibility for radial tensile failure exists. McLean and Addis reviewed strength criteria used in many published models and showed that certain criteria do not stand up when compared with laboratory rock strength test data. Therefore, they highlighted the effect of strength criteria on mud weight selection showing some of the anomalies and contrary evidence which can make the choice of a strength criterion difficult and confusing when performing wellbore stability analysis. Based on the laboratory data, they recommended the Mohr-Coulomb criterion as the most realistic. P. 483
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.