Productivity of Inside Casing Gravel-Pack Completions

Abstract

This study of flow resistances imposed by gravel packing a cased well shows that the greatest resistance is often through the sand-filled perforations. Field test data verify that increasing perforation area perforations. Field test data verify that increasing perforation area can increase productivity. Introduction Creole Petroleum Corp. produces from several unconsolidated or poorly consolidated reservoirs of Miocene age that require a sand control treatment at some time during their producing life. Initial attempts to control sand employed various wellbore bridging devices that either were unsuccessful at controlling sand production or severely restricted well productivity. Preperforated pipe, for example, did not productivity. Preperforated pipe, for example, did not provide adequate sand control, so that wells had to be provide adequate sand control, so that wells had to be produced at low rates. Screen liners with openings produced at low rates. Screen liners with openings larger than 0.01 in. did not prevent production of sand and when 0.01-in. openings were used, severe plugging and restriction of flow occurred. plugging and restriction of flow occurred. Gravel packing, which Creole started using as a sand-control measure in the early 1950's, had become the standard method of controlling sand by the late 50's. Gravel-pack completions normally are of the following types: open-hole gravel pack, inside casing gravel pack, or inside casing gravel pack with a high-pressure sand squeeze preceding the gravel pack (see Fig. 1). The open-hole pack is used when the completion is in a single sand or when multiple sands can be produced without fear of gas or water production. The cased-hole pack is most often used when production. The cased-hole pack is most often used when multiple sands are to be produced through a single tubing string. The relative productivity of the various completion techniques is illustrated in Table 1, which presents measured productivity indices data for presents measured productivity indices data for two reservoirs. Note that wells completed with a gravel pack inside a cased hole have severely limited productivity. productivity. Although many things influence production from gravel packed wells, two of the main limiting factors are (1) invasion of fine formation sand into the pack and (2) flow restrictions imposed by the gravel-packing operation. These mechanisms are illustrated by production data shown in Fig. 2. The well was production data shown in Fig. 2. The well was initially completed with a cased hole and perforated with four 1/2-in. perforations per foot of sand. After flowing for several months at about 2,000 BOPD the well began to produce sand. The treatment used to control the condition consisted of a high-pressure sand-oil squeeze (SOS) and inside gravel pack (IGP) retained by a slotted liner. In conjunction with this treatment, the well was equipped with gas-lift valves and afterwards was produced by gas lift. The abrupt drop in rate following the sand control treatment is associated with the restrictions to flow imposed by the gravel-packing operation and was probably caused by plugging of the gravel pack probably caused by plugging of the gravel pack by formation fines. To combat the problem, smaller gravel is used, so that currently it is about five to six times the size of the smallest formation sand in the 10 to 70 percentile region of the distribution. This selection procedure is similar to that proposed by Schwartz and by Maly and Krueger. Formation sand size distributions and the gravel size that would be selected to control sand are illustrated in Fig. 3. In this example, the grain size ratio is about 5.1 at the 10-percentile point, 5.7 at the 40-percentile point, and 6.1 at the 70-percentile point. JPT P. 419