Study and Field Application of New Agent for Casing Repair in High Temperature and High Salinity Reservoir

Abstract

Casing failure probability is high in Tarim Oilfield, due to high pressure high temperature and high sality operational environment, near 6% of total wells were damaged during their production life, which has serious impacts on the development well pattern, resulting in unbalanced injection-production. Based on the analysis of the situation and distribution of casing damage in the Tarim Oilfield, which located in northwest of China, was discovered in 1989, Its production formation has unwanted characteristics of high temperature (150°C) and high salinity (250000mg/L), in order to treatment the casing damage wells, a new type of chemical plugging agent named LTTD was synthesized on the basis of LTSD and its resistance to acid, temperature and salinity were carried out by experiments to evaluate the property of new chemical plugging agent. The plugging strength of LTTD and G-grade cement solidified body in different periods was studied by simulating the actual conditions of Tarim Oilfield, the mechanical properties of adhesive interface between LTTD and G-grade cement under dynamic condition were evaluated and microscopic observation of adhesive interface under dynamic condition were carried out. The experimental results show that the new plugging agent is characterized by marked improvement of performance and the enhanced resistance to acid, high salinity and high temperature conditions, moreover the formation of "the interpenetrating network structure" with high pressure bearing capacity in short time. In the actual condition of Tarim Oilfield, the plugging strength of LTTD plugging increase with the increase of temperature, which is higher than the strength of G-grade cement, during dynamic process, LTTD plugging is superior to G-grade cement in less amount of dissolution of calcium in hydration process and in better anti-channeling performance. Microscopic observation shows that both the inner and the bonding surfaces of the LTTD blocking agent have compact microstructure, which could effectively avoid the excessive formation of hydration product on bonding interface, and could produce hydration products against erosion, with strong self-healing ability and improve plugging quality. Field tests show that not only repair casing damage successfully, but also promote the oil production. Therefore, the development of new plugging agent can improve the ultimate recovery of Tarim oilfield. This article provides a type of plugging agent for solving the casing damage and the result may be valuable to develop the similar oilfields.