Design, Plan, and Execution of Gravel-Pack Operations for Maximum Productivity

Abstract

During the past 6 years, there have been several significant improvements in gravel-pack techniques. This paper reviews some of these improvements and discusses some other factors that should be considered in a gravel-pack application. Introduction Sand production in Louisiana Gulf Coast Miocene wells has been a serious problem since the development of fields in this area began. It is a more serious problem today with the high production rates allowed and the development of younger sands that appear to be finer and contain more silt and clay particles. Much of the research in the early studies of sand control by gravel packing was pointed toward sands with a relatively small amount of fine sand pointed toward sands with a relatively small amount of fine sand and silt. Sands of this type are relatively easier to control because the main concern is determining a gravel size that will restrain the formation sand. The reduction of pack permeability by fines earlier was thought not to be serious because the gravel had extremely high permeability and the interface between the formation sand and gravel had substantially the same permeability as the formation sand. This is not the case in most of the unconsolidated sands found in the Gulf Coast area. It has been demonstrated that invasion of the pack by fine sand can have a serious effect on well productivity. For this reason, the gravel has been sized to minimize the invasion problem. However, the use of smaller gravel requires more careful planning in the design and execution of the job. The use of smaller gravel may require a larger perforation area or, in some cases, an open-hole completion may be required. Smaller gravel is also more susceptible to permeability reduction caused by mixing with perforation debris and formation sand during placement, New perforation debris and formation sand during placement, New placement techniques have helped to solve the contamination placement techniques have helped to solve the contamination problems while performing the gravel pack. Productivity in problems while performing the gravel pack. Productivity in gravel-packed wells also may be impaired by the use of completion fluids that are damaging to the gravel pack. In wells where the reservoir pressure gradient is greater than 0.61 psi/ft, it has been common practice to complete with drilling mud. The reason for this practice was that a safe, nonpolluting brine was not available. The development of calcium-chloride/calcium-bromide brine has made it possible to complete wells with pressure gradients up to 0.785 psi/ft using a low-solids workover fluid. Gravel-Size Selection One of the most important aspects of designing a gravel pack for maximum productivity is selection of the gravel to be used. Where formation samples are not available, a blanket recommendation would appear to be to use the smallest gravel possible without restricting productivity. When representative samples are available, size selection can be based on formation particle-size distribution. To assure effective sand control and longer-lived gravel packs, it appears that the gravel should be sized to prevent invasion of the gravel pack by the finest formation sand. The particle-size distribution generally is obtained by sieve analysis of formation samples. The frequency and type of samples taken have been shown to be of considerable importance. Of the several types of samples available, rubber-sleeve cores generally are accepted to be the most representative. A sample taken from production lines or equipment can contain excess fines because of production lines or equipment can contain excess fines because of hydraulic separation. JPT P. 1259