Consolidation of Dirty Sands by Phenol-Formaldehyde Plastic

Abstract

Two organic chemicals anhydrous n-hexanol and ethylene glycol monobutyl ether have been developed as preflushes. The proper use of either of these compounds improves the injectivity, permeability retention, and compressive strength of formation sands consolidated with phenol-formaldehyde plastic. Introduction Plastics have been widely used to control sand Plastics have been widely used to control sand production. The popularity of the process derives production. The popularity of the process derives from its inherent convenience and from favorable performance characteristics: the wellbore is left performance characteristics: the wellbore is left unobstructed, there is no casing size limitation, and currently available plastics are strong and possess a high degree of chemical inertness. The possess a high degree of chemical inertness. The fact, also, that the injection of plastic behind the casing results in the formation of a relatively large filter area is another important feature. A large filter area is beneficial because the hydrodynamic forces acting at some distance from the wellbore are minimized, and the filter matrix, composed of plasticized formation particles, is relatively resistant to plugging caused by mobile formation particles from outside the plasticized region. In dirty sands (those with an appreciable nonquartz content), however, successful consolidation has been difficult to achieve. This has been attributed to the higher surface area presented by this type of formation, which results in either inadequate plastic coverage of the interval treated (reflected in low set strength) or inadequate penetration of the plastic. Clay-containing formations are also susceptible to permeability reduction caused by contact with extraneous permeability reduction caused by contact with extraneous water. Although precautions can be taken to minimize water influx into sensitive formations, it is almost inevitable that some water contact will occur for example, when a sand-filled wellbore is being cleared by washing. The set plastic by itself reduces permeability somewhat, and any reduction due to permeability somewhat, and any reduction due to contact with water constitutes a further difficulty in plastic consolidation of dirty formations. The plastic consolidation of dirty formations. The permeability of the plasticized region is important permeability of the plasticized region is important not only with regard to well productivity, but by increasing the pressure drawdown necessary for a given production rate, permeability reduction shortens the life production rate, permeability reduction shortens the life of the plastic job. Laboratory Test Procedure Formation Samples To make the results of this study as applicable to field operations as possible, we used rubber sleeve core barrel samples of formation material rather than of synthetic blends. For comparison, some experiments were conducted in which a clean, high-silica sand was consolidated. Also, in a few instances, produced sand samples instead of pressure core barrel samples were employed. We first cleaned the formation samples slightly by removing obviously extraneous material, and then we air-dried them in an oven. Some of the sample characteristics, including clay mineral content measured by X-ray diffraction, are shown in Table 1. Sample A was unusually difficult to plastic-consolidate; for this reason, it was particularly useful in this study. The data of Table 1 indicate the total clay mineral content of this sample to be 6.2 percent, which is not unusually high; but the nonquartz content (feldspars, calcite, and clay minerals) was 33.2 percent, which is quite high. Clay mineral content is the percent, which is quite high. Clay mineral content is the sample characteristic to which relative ease or difficulty of consolidation has generally been attributed. JPT P. 934