No abstract

Drilling-induced formation damage is the key factor dominating the failure of development of hydrocarbon reservoirs with low-permeability. In this paper, a new low-damage drilling fluid was formulated, evaluated, and applied to well drilling operations in a low-permeability reservoir in the Shengli Oilfield, China. To formulate this low-damage drilling fluid, filter-cake forming agents were used to prevent fluid loss, inhibitors were used to enhance the shale inhibition of the fluid, surfactants were used to minimize water block, and inorganic salts were used to enhance compatibility. A holistic experimental approach combining Micro-CT, SEM, FT-IR, and XRD techniques was designed to identify the underlying interactions between the formulated drilling fluid and rock samples, demonstrating its significant mitigation on formation damage which mainly results from the hydration of clay minerals and the invasion of solid particles. The newly formulated low-damage drilling fluid is then extended its applications to well drilling operations with excellent performance. Not only can the new low-damage drilling fluid avoid non-fracturing stimulation, but also reduce the drilling operational costs and time, minimize the formation damage, and facilitate extending the reservoir life for a longer time.

To address present concerns about thickening time and high early-strength in deepwater cementing at low temperatures when using conventional accelerators, a new type of set-accelerating admixture comprising of lithium chloride, aluminium hydroxide and alkaline metal chlorides, named as LS-A, was studied in this paper. Mechanism analysis and performance tests show that the accelerator LS-A accelerated the hydration of tri-and dicalcium silicates (C 3 S and C 2 S) at low-temperatures by speeding up the breakdown of the protective hydration fi lm and shortening the hydration induction period. Therefore, LS-A could shorten the low-temperature thickening time and the transition time of critical gel strength from 48 to 240 Pa of the Class-G cement slurry, and improve the early compressive strength of set cement at low-temperatures. It exhibited better performance than calcium chloride and had no effect on the type of hydration products, which remain the same as those of neat Class-G cement, i.e. the calcium silicate gel, Ca(OH) 2 crystals and a small amount of ettringite AFt crystals. LS-A provides an effective way to guarantee the safety of cementing operations, and to solve the problems of low temperature and shallow water/gas fl owing faced in deepwater cementing.