Stability shales

Sodium chloride has long been used as a shale stabilizer because of low cost, wide availabiUty, and its presence in many subsurface formations. The inhibitive nature of salt muds increases as the salt content increases from seawater to saturated sodium chloride. In addition to the sodium chloride consumed aimuaHy for drilling fluid, considerable quantities are incorporated while drilling salt zones. This material has been used more for minimizing washouts in salt zones than for stabilizing shales. High salt levels have found appHcation in deep water drilling (7). 

Ammonium chloride [12125-02-9], ammonium sulfate [7783-20-2], and diammonium phosphate [7708-28-0] have also been used for shale stabilization (102,103). Ammonium ions have essentially the same effect on shales as potassium ions but use of ammonium salts is often objectionable because of the alkaline nature of the mud. In the North Sea and northern Europe, where magnesium-bearing salt formations ate encountered, magnesium chloride [7786-30-3] is used, but in the United States it is used only on a small scale. 

Sohd materials, such as gilsonite and asphalt, and partially soluble sulfonated asphalt may also be added to plug small fractures in exposed shale surfaces and thereby limit water entry into the formation (105,124). The asphalts are oxidized or treated to impart partial solubiUty. These materials may be softened by the downhole temperature, causing them to deform and squeeze into small openings exposed to the borehole. Laboratory tests designed to evaluate shale-stabilizing muds have confirmed the beneficial action of these materials (125) (see also Soil STABILIZATION). 

Selected clay stabilizers are shown in Table 1-10. Thermal-treated carbohydrates are suitable as shale stabilizers [1609-1611]. They may be formed by heating an alkaline solution of the carbohydrate, and the browning reaction product may be reacted with a cationic base. The inversion of nonreducing sugars may be first effected on selected carbohydrates, with the inversion catalyzing the browning reaction. 

There are special shale stabilizing surfactants consisting of nonionic alkanol-amides [900, %2], for example, acetamide monoethanolamines and diethanolamines. 

Shale stability is an important problem faced during drilling. Stability problems are attributed most often to the swelling of shales. It has been shown that several mechanisms can be involved [680,681]. These can be pore pressure diffusion, plasticity, anisotropy, capillary effects, osmosis, and physicochemical alterations. Three processes contributing to the instability of shales have to be considered [127] ... 

Clays or shales have the ability to absorb water, thus causing the instability of wells either because of the swelling of some mineral species or because the supporting pressure is suppressed by modification of the pore pressure. The response of a shale to a water-based fluid depends on its initial water activity and on the composition of the fluid. The behavior of shales can be classified into either deformation mechanisms or transport mechanisms [1765]. Optimization of mud salinity, density, and filter-cake properties is important in achieving optimal shale stability and drilling efficiency with water-based mud. 

One potential mechanism by which polymers may stabilize shales is by reducing the rate of water invasion into the shale. The control of water invasion is not the only mechanism involved in shale stabilization [133] there is also an effect of the pol5maer additive. Osmotic phenomena are responsible for water transport rates through shales. 

S. E. Alford. North Sea field application of an environmentally responsible water-base shale stabilizing system. a Proceedings Volume, pages 341-355. SPE/IADC Drilling Conf (Amsterdam, the Netherlands, 3/11-3/14), 1991. 

C. Aviles-Alcantara, C. C. Guzman, and M. A. Rodriguez. Characterization and synthesis of synthetic drilling fluid shale stabilizer. In Proceedings Volume. SPE Int Petrol Conf in Mex (Villahermosa, Mexico, 2/1-2/3), 2000. 

H. Branch, III. Shale-stabilizing drilling fluids and method for producing same. Patent US 4719021,1988. 

M. Fu and X. Hu. An investigation into shale stability by utilizing copolymer of acrylamide and acrylonitrile and its derivatives. JJiang-han Petrol Inst, 19(l) 70-73, March 1997. 

M. Jarrett. Nonionic alkanolamides as shale stabilizing surfactants for aqueous well fluids. Patent WO 9632455, 1996. 

Cydril [Cytec]. TM for a drilling mud additive, shale stabilizer and viscofier. 

Sun Y, Liu P, Song W and Gai X. 1998. Mechanics and Chemistry coupled model of shale stabilization in deviated hole. Petroleum Drilling Technology, 26(4), pp. 51-53. 

This article will try to clarify relevant physical processes in shale stability in drilling. However, a quantitative framework for coupling stress-strain-strength behavior and transport processes in shale must be based on induced volume changes, and this issue is not explicitly discussed. 

Conversely, processes that increase o, tend to have stabilizing effects combined with geochemistry, this forms the basis of much shale stabilization efforts during drilling (i.e. higher mud densities). 

Figure 2. Size orientation affect shale stability Scale factors and fissility effects...

Chem. Descrip. Methyl glucoside CAS 97-3(T3 EINECS/ELINCS 202-571-3 Uses Chem. intermediate for improving processing char, and props, in oil drilling muds for onshore and offshore drilling, soap/cosmetics, urethane foams, phenolic adhesives, textiles, surf, coatings shale stabilizer... 

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