Problems Related to Squeeze Cementing

Abstract

Causes of problems relating to squeeze cementingoperations are presented. Much has been written on materialsand techniques that have been used in particular areas, but little mention is made of some problems that occurduring the operation.Squeeze cementing generally can be described as theprocess of forcing a cement slurry into holes in the casingand cavities behind the casing. These operations areusually performed during drilling and completion of a well, or for repairing or altering a well at some later date. Squeeze cementing is necessary for many reasons, butprobably the most important use is to segregate hydrocarbonproducing zones from those formations producing otherfluids. The key factor on a squeeze cementing job is thatof placing the cement at the desired point or pointsnecessary to accomplish the purpose.Squeeze cementing problems are closely related to man'sability to understand the earth's properties once its crusthas been penetrated. It is often difficult to determine whysome wells can be squeezed successfully with one job whileothers in the same field require four or five jobs. Thereseem to be a number of opinions as to the proper methodof squeeze cementing. We are not attempting to argue orfind fault with these opinions; rather we hope to approachand recognize problems that do occur in such a mannerthat we might learn to consider ways in which to solvethem.Applications of Squeeze CementingSome of the most pertinent applications for squeezecementing that need consideration are:supplementing aprimary cementing job that may be deficient because ofchanneling or insufficient fillup (Fig. 1);reduction orelimination of water intrusion from above or below thehydrocarbon producing zone (Fig. 3);reduction of theGOR by isolating the oil zone from an adjacent gas zone;repair of a casing leak that might have developed due tocorrosion, pressure parting or joint leaks (Fig. 2); andabandoning of old perforations or plugging of a depleted orwatered-out producing zone.The language used in squeeze cementing is rather looseand subsequently leaves much to the imagination of thoseexpected to execute the job. During training sessions heldby one of the major oil companies the past 2 years, drilling people were presented with the question, "What isyour definition of a breakdown?" Recognizing that amajority of those present were from California oil fields, andthat the major application for squeeze cementing is thatof supplementing a faulty primary job to obtain isolationof an oil zone from adjacent water zones as required bythe California Division of Oil and Gas, the type of squeezejob that was foremost in their minds was that of squeezingwater-shutoff holes. There were two definitions expressedmost frequently:That pressure necessary to break down or fracturethe formation so that it will accept fluid.That which must he done before one can attempta squeeze cementing job.Breakdown actually is a poor name for what really needsto be attained on most squeeze jobs since the prominentproblem is in the wellbore, and the desired performanceis for the perforations and cavities to accept fluid withoutfracturing. Fractures normally will accept the cementslurry and often great volumes of it, but not necessarily inthe area that needs repair. Obtaining a fracture on thebreakdown will more often than not cause extra rig time.require greater volumes of cement, and create lost timewaiting on cement-all of which are costly.A term closely related to breakdown and one that needsto be understood is formation fracture gradient which isthe pressure/foot of depth required to create a fracture. Also of interest is the fact that propagation and extensionof a fracture usually require a lower pressure than wasneeded for its creation. Too often it is assumed thatoverburden lifting is necessary for a fracture to occur. Also, due to average formation density, the fracturinggradient is anticipated to be at least 1 psi/ft of depth. This is a good round number and easy to use in calculations, but experience has indicated that due to structural stresses inthe earth and elasticity of the earth's formations, fracturesusually occur at less than 1 psi/ft and often as low as 0.6psi/ ft.JPTP. 801ˆ