Experimental Evaluation of Transition Metals Salt Solutions as Additives in Steam Recovery Processes

Abstract

Abstract It is well documented by laboratory and field data that besides physical changes such as viscosity reduction with temperature and steam destilation, the steam injection processes are accompanied by chemical reactions which, as it has been the case in the M-6 steam drive project in the Bolivar Coast of Lake Maracaibo, produce large amounts of undesirable hydrogen sulphide gas. Depending on the type of crude and on the steam temperature, they can also produce an irreversible increase or lowering of crude oil viscosity. To in-situ control the hydrogen sulphide production and to promote the lowering of the crude oil viscosity, it has been proposed to use transition metals salts solutions such as nickel sulphate as additives in steam injection processes. In this work, we present the results of an experimental study present the results of an experimental study carried out to assess the effect of using such an additive. The experimental plan consisted of both static and dynamic test. The concentration of the solution was varied to 1.5 wt. % nickel sulphate at a temperature of 240 degrees C, typical of Venezuelan steam injection projects. Reconstituted and whole core samples from projects. Reconstituted and whole core samples from two Venezuelan bitumen reservoirs were used. Obtained results show that the two bitumen samples undergo aquathermolysis, in presence or absence of reservoir sand, that results with reconstituted sands are similar to those obtained with whole core samples and that the use of the additive promotes a lowering in bitumen viscosity, both in static and dynamic test. In the dynamic tests, however, changes are more pronounced in shorter reaction times. In one case the oil viscosity was lowered 20 times. Introduction Steam injection processes, both cyclic and drive, are the most successful enhanced oil recovery methods, accounting for around 80 percent of the oil produced by EOR projects in the U.S.A. and almost 100 percent of that produced in Venezuela. The success of this processes is mainly the result of physical phenomena such as temperature raise, viscosity reduction, steam distillation, etc. This has led to the widely accepted view that the primary, if not sole consequence of injecting high primary, if not sole consequence of injecting high temperature steam into heavy oil formations is physical. However, it is well documented by laboratory physical. However, it is well documented by laboratory and field data that steam injection processes are also accompanied by chemical processes are also accompanied by chemical reactions which as it was pointed oil before produce large amounts of gases and change crude oil produce large amounts of gases and change crude oil viscosity. Hyne used the term aquathermolysis to describe the reactions occurring in the 200 degrees C - 300 degrees C temperature range, and which may include acid polymerization, organosulphur compounds cleavage due to reaction with water, gas release from both the fluids and rock matrix, the water gas shift reaction and hydrodesulphurization. Other authors have studied the thermal visbreaking of heavy oils and bitumens in the 260 degrees C 325 degrees C temperature range. P. 539