Introduction:Drilling fluid selection plays a key role in preventing major problems encountered during drilling operations such as hole pack-off, stuck pipe and loss circulation. Mud contamination which results from the overtreatment of the mud system with additives or foreign material entering the mud system during drilling operations causes unwanted changes in the properties of the mud. This makes the mud system inefficient in performing its major roles. This research studies the effects of monovalent and divalent salts namely Potassium Chloride, Calcium Chloride, and Magnesium Chloride on the rheological properties of water-based mud system which is most vulnerable to contamination.Methods:Sixteen mud samples were formulated of which fifteen were contaminated each with different concentrations (0.75 g, 1.50 g, 2.50 g, 3.50 g, and 5.0 g) of the various salts at ambient temperature.Results:The results showed that the rheological properties such as plastic viscosity, apparent viscosity and yield point of the mud samples decreased as the concentrations of various salts increase.Conclusion:It was concluded that increase in the concentration of the salts resulted in a decrease in the rheological properties of the mud samples. This indicates that with the monovalent and divalent salt contamination, there is a significant decline in the performance of drilling mud since the salts affect the dispersion, hydration and flocculation behaviour of the particles. The effect was more profound with CaCl2 and MgCl2 salts than the KCl salt.
Predicting pressure distribution in a petroleum reservoir is principal to the reservoir's evaluation and maintenance, as pressure changes with space and time. A convenient approach to effectively achieve this task is to formulate fluid flow equations based on the reservoir characteristics and solve them numerically. Numerical method provides solutions to mathematical fluid flow models developed in a reservoir simulation. This study provides numerical solutions, using both finite difference explicit and implicit method, to a mathematical model by developing MATLAB codes to ascertain the pressure distribution for a singlephase, one-dimensional, slightly compressible fluid flow in a petroleum reservoir. Series of numerical simulations were carried out during the first year of production using timestep sizes of 1, 2 and 3 days, respectively. The explicit method gave poor result (negative values for pressures) for timestep of 1 day, an outcome that is not accurate to describe the problem being solved but gave acceptable pressure results for timestep of 2 and 3 days. This shows that the efficacy of the explicit method is reliant on the chosen timestep and simulation time. In contrast, the implicit method gave a quite satisfactory results for all timesteps, and including less than 1 day, confirming the robustness and unconditionally stable nature of the implicit method. A commercial simulator (CMG software) was also employed to build a one-dimensional black oil model to validate the aforesaid results of which a close match was observed between the simulator results and the numerical solutions. This study provides insights to reservoir's pressure profile during hydrocarbon recovery beforehand so that efficient pressure maintenance decisions can be made to achieve economic hydrocarbon recovery throughout the life of the reservoir.
Presently, analytical models for estimating reservoir parameters for solution gas-drive are restricted to either constant pressure or constant rate assumption. Thus, current models for solution gas-drive do not allow for rigorous analysis of simultaneous variations in pressure and rate. In addition, the traditional material balance time or pseudotime, which models variable pressure and/or variable rate case, is limited to single-phase flow. This paper proposes a normalized multiphase pseudotime function that is capable of modeling general variable pressure and/or variable rate data for solution gas drive reservoirs during boundary-dominated flow. In particular, we present a multiphase flow equation that incorporates this pseudotime function. This flow equation is expressed in a form that traces the rate/time harmonic depletion curve. Thus, the proposed approach allows analysts to use a single depletion curve to model constant rate, constant pressure and variable pressure/variable rate cases for solution gas drive reservoir systems. In addition, we propose a multiphase pseudocumulative function that is normalized by pseudopressure drop to permit the extension of flowing material balance method to solution gas drive. This is essential since analysis using flowing material balance method offers a better resolution than decline type curves. It also permits the computation of initial-oil-in-place. The significant contribution of this paper is the generality of the proposed model that allows the rigorous handling of variable pressure and/or variable rate case for solution gas drive reservoir systems. Thus, the proposed approach, as opposed to existing models, is not limited to production constraints. Only the appropriate equations and the methods of analyses and interpretation are presented in this paper. Illustrative examples are deferred to a subsequent writing.
The environmental challenges posed by conventional oil-based drilling fluids along with legislation associated with their use have necessitated the development of synthetic organic liquids that are designed to improve environmental protection. In this research, waste/used oils from restaurants and food joints have been tested for their potential use as synthetic based fluids through rheological analysis. Physiochemical properties of the waste vegetable oil were determined; density: 0.88g/cm3, acid value: 64.8mg KOH/g of oil and Free Fatty Acid (FFA) content: 32.4%. The optimum conditioning of biodiesel production from waste oil was in two-step catalysed process. In the first step, sulfuric acid was used as a catalyst for esterification reaction to reduce acid value of the oil below 3mg KOH/g which was with different dosages. The next step was the base catalysed transesterification process which converted the pre-treated oil into biodiesel and glycerol in the presence of methanol and NaOH at varied reaction conditions. Density of 9.1 lb/gal and rheological properties; Yield Point (17 Ib/100ft2, 2 Ib/100ft2 and 2 Ib/100ft2), Plastic Viscosity (17cP, 8cP and 6cP), Gel strength at 10Ȳ (3 Ib/100ft2, 2 Ib/100ft2 and 2 Ib/100ft2) and Gel strength at 10″ (5 Ib/100ft2, 4 Ib/100ft2 and 2 Ib/100ft2) were all determined at temperatures of 80°F, 120°F and 160°F respectively. The formulated mud showed that biodiesel is a promising synthetic based fluid and has most of its rheological properties meeting the API standard. Though the initial cost of conditioning biodiesel will be quite high, it can be offset by its disposal cost as compared to that of diesel.
In the estimation of most reservoir parameters in well test, the reservoir is assumed to be isothermal which is practically not true due to the fact that there are heat sources from friction in the wellbore, work done by the drill bit and as well as thermal recovery. Although, this temperature change is small, it can serve other beneficial purposes in the reservoir and the wellbore. The research work used the small change in temperature to estimate reservoir parameters like permeability and skin factor. This research work brought out equations to be used in the estimation these reservoir parameters and the applied to field data. This research work is applicable in reservoirs where steam flooding and in situ combustion processes are used as the enhanced oil recovery methods. These result obtained for permeability was practically the same as the true reservoir permeability from field data although the same could not be said about the skin factor since that of the estimated and true value were quite different. This makes thermal transient testing a good substitute for the estimation of reservoir permeability. The same could not be said about the skin factor since it affect the pressure drop not temperature change. This research work brought out the idea that thermal transient testing can be used as a tool for estimating some reservoir parameters as well as verification for estimated reservoir parameters using other well test methods.
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