Remedial Cementing Of Plugged Perforations
Authors: Carter L.G. , Harris F.N. , Smith D.K. 
Published: December 2007

This paper is to be presented at the California Regional Meeting of the Society of Petroleum Engineers of AIME in Santa Barbara, Calif., on Oct. 23–25, 1963, and is considered the property of the Society of Petroleum Engineers. Permission to publish is hereby restricted to an abstract of not more than 300 words, with no illustrations, unless the paper is specifically released to the press by the Editor of JOURNAL OF PETROLEUM TECHNOLOGY or the Executive Secretary. Such abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in JOURNAL OF PETROLEUM TECHNOLOGY or SOCIETY OF PETROLEUM ENGINEERS JOURNAL is granted on request, providing proper credit is given that publication and the original presentation of the paper.
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Abstract
The development of efficient low water loss additives has greatly improved the effectiveness of squeeze cementing. Selective perforating using non-plugging perforating fluids also has aided the success of squeeze cementing. However, specialized mud systems, such as those treated with ferrochrome lignosulfonates, inverted oil emulsions, and oil base fluids pose problems in squeezing perforations. This paper describes laboratory model studies of squeezing perforations blocked with these types of mud systems. Effective removal of these drilling fluids from the perforations by use of chemical washes ahead of the cement system is depicted.

Introduction
Chemical washes to remove the drilling mud ahead of a cement slurry on primary cementing jobs have been successfully used for many years, though not universally accepted. However, the use of these materials in conjunction with squeeze cementing is relatively uncommon. With the development of specialized mud systems the number of squeeze jobs required to seal off a set of perforations has generally increased. Concurrently, the introduction of low fluid loss cements has decreased the number of squeeze jobs necessary for successful shut-off of perforations. Nevertheless, remedial results in many areas of the country still leave something to be desired. In most instances when a formation is perforated with something other than a non-damaging perforating fluid, only a part of the perforations will produce fluid. This fluid will be produced from the most permeable sections. As a result, these perforations would be more likely to accept cement during a squeezing operation. Other perforations being dormant during the producing phase could be contaminated in some manner or have reduced permeability. Even though no fluid was produced prior to the initial squeezing of they become active and produce to relieve formation pressures after the more permeable zones have been cemented. These conditions sometimes require multiple squeeze stages to obtain a complete seal of all perforations. The intent of this paper is to present data obtained in a series of laboratory investigations of the practices associated with spotting a flush across a perforated interval prior to squeezing. Results of these tests indicate a much better chance for the cement to seal perforations which are void of contamination. The ability of various solutions to chemically react with drilling muds or other contaminating materials blocking the perforation, thus allowing slurry to enter all perforations, enhances the possibility of a successful squeeze job. The success of these solutions on multiple perforations will depend upon the competence of the flush to chemically attack the particular mud system. This results in partial equalization of the rate and pressure at which some fluid can enter each perforation prior to placement of the cement slurry. Even though the less permeable perforations accept a very small quantity of the treating solution compared to the more open sections, it is still adequate to aid in forcing the dormant perforations to accept the cement slurry. The use of low filtration rate cement slurries to obtain better squeeze jobs has been relatively common for several years. This type of slurry tends to prolong dehydration of cement inside the pipe - a condition which can occur across perforations in more permeable zones. This control of dehydration tends to keep the cement in a fluid state allowing it to move across, and into, all perforations during a squeeze job. Also, a low fluid loss cement minimizes the node build-up at the perforation as compared to a high filtration rate slurry.
The authors do not plan to discuss the different methods of squeeze techniques; however, previous work by Beach, O'Brien and Goins indicates that excessive pressure during a squeeze job may cause fracturing of the formation and allow cement displacement into this fracture.