Ultrafine Cement for Oilwell Cementing

Abstract

Abstract Ultrafine cements are particulate, cementitious grouting materials that were initially developed as a replacement for unacceptably toxic chemical grouts for Civil Engineering applications. Several basic types are available: ultrafine slag cement (Ml), ultrafine portland cement (M3) and ultrafine portland/slag (M5). The chemical compositions and physical properties of these materials are shown in Table 1 and 2 and in Figure 1. Their extremely fine grain size enable them to permeate medium sands and fine fractures in rock. These and other properties have led to ultrafine M5 cement slurries being adopted for use in oilwell cementing applications, especially for gas and water control. The results of a series of experiments on ultrafine M5 cement slurry have indicated that it remains in a fluid state at high temperatures for at least as long as slurries formulated with Class G Portland cement, demonstrating its applicability for use in hot, deep wells. Applications for M5 involve squeeze cementing the Wasson South Unit 7514 casing leak at 3222 feet. 30 sacks of M5 were successfully used to seal the casing leak as the ultrafine cement was drilled out and the casing tested to 1000 psi with no bleed-off. In another application, M5 ultrafine cement was used to squeeze repair a casing leak. The previously repaired leak had broken down and was taking lift gas and giving up sour water. M5 was used to seal the leak and restored top allowable, water-free oil production from the well. Introduction The ultrafine cements are particularly suited for oilwell squeeze cementing because of their very fine particle size, low settlement, medium viscosity, long initial hardening time and durability. Ultrafine cements may be used for the following squeeze cementing applications: Reduce High GOR (Gas/Oil Ratio)Control Excess Water Repair Casing Leaks Seal Off Thief Zones Protect Against Fluid Migration Ultrafine cements are cementitious grouting materials composed of ultrafine particles of slag and portland that exhibit excellent penetrability, strength and durability suitable for squeeze cementing of oilwell matrices, especially for gas (GOR) and water (WOR) control. The following properties of the ultrafine cements may be utilized for oilwell squeeze cementing: Permeating Power Ultrafine particle size (maximum 2 percent greater than 10 microns) allows the grout to permeate fine sands and finely fractured rock. High Strength Ultrafine slag is activated with portland cement to achieve high strength at low density. Excellent Durability After hardening, ultrafine cement grouts acquire high impermeability protecting them from sulfate and chloride attack. Long Initial Hardening Time Ultrafine slag/portland cement grout provides long fluid time at high temperature and pressure for maximum permeation of the oilwell matrix. Low Settlement Rate Ultrafine cement's fine particle size eliminates early hard settlement of larger particles, its fine particles remain in suspension because of medium viscosity. Chemical compositions of the ultrafine cements are described in Table 1.0. M5 consists of a blend of ultrafine portland and slag cements. M1 is 100 percent ultrafine slag and M3 is 100 percent ultrafine portland. Because of its very slow hardening reaction, M1 cannot be use alone below 20 deg C and must be used with at least 25 percent portland to initiate the hardening reaction. M1 may be used alone above 20 deg C because higher oilwell temperatures initiate the slag hardening reaction especially with small amounts of sodium hydroxide. P. 291^