Simulation of High-pH Coreflood Experiments Using a Compositional Chemical Flood Simulator
- D. Bhuyan (Unocal Corp.) | G.A. Pope (U. of Texas) | L.W. Lake (U. of Texas)
- Document ID
- Society of Petroleum Engineers
- SPE International Symposium on Oilfield Chemistry, 20-22 February, Anaheim, California
- Publication Date
- Document Type
- Conference Paper
- 1991. Society of Petroleum Engineers
- 5.5 Reservoir Simulation, 5.5.8 History Matching, 5.2.1 Phase Behavior and PVT Measurements, 4.1.5 Processing Equipment, 4.1.2 Separation and Treating, 5.6.5 Tracers, 1.6.9 Coring, Fishing, 5.2 Reservoir Fluid Dynamics, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 5.2.2 Fluid Modeling, Equations of State, 4.3.4 Scale, 5.4.1 Waterflooding, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.3.2 Multiphase Flow
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This paper reports on the use of a high pH chemical flood reservoir simulator to simulate high pH coreflood experiments. The coreflood experiments include one alkaline flood, two alkaline/polymer floods under two different salinity environments and an alkaline/surfactant polymer flood. The agreement between the experimental and numerical oil recoveries and produced chemical compositions is very encouraging and supports the validity of the mathematical model used in the simulator. The importance of the preflush brine salinity. mobility control and effective salinity gradient using a cosurfactant as observed in the experimental data are also evident from the numerical results. Most of the fundamental mechanisms known for micellar/polymer flooding also seem to apply to high pH chemical floods, especially the dominant effect of low interfacial tension. This is the first time that comparisons have been made between a mechanistic reservoir simulator and high pH coreflood experiments. Such comparisons have yielded new insights into high pH chemical flooding.
Over the past decade, considerable progress has been made in the understanding and modelling of high-pH chemical flooding processes. As opposed to flooding with only alkaline processes. As opposed to flooding with only alkaline solutions. researchers have used polymers and external surfactants along with the high-pH chemicals to produce synergistic effects on oil displacement. These studies indicate a close parallel between the displacement mechanisms in high-pH floods and those known for the micellar/polymer process. The alkaline processes, however, suffer from process. The alkaline processes, however, suffer from additional complications because of the large reactivity of the alkaline chemicals with the reservoir rock and fluids. These reactions affect the transport and physical properties of these processes to a great extent. The mathematical models used to processes to a great extent. The mathematical models used to simulate these pH floods must include these effects.
With this goal in mind, we have extended a compositional simulator, UTCHEM, developed initially to simulate micellar/polymer floods, to model high-pH chemical floods. Results of several hypothetical high-pH chemical flood simulations were in qualitative agreement with most of the experimental observations.
Perhaps the most basic assumption used in UTCHEM is that of Perhaps the most basic assumption used in UTCHEM is that of local thermodynamic equilibrium (LTE), wherein it is assumed that the fluid and solid surfaces are in equilibrium wherever and whenever they are in contact. Though not generally true, LTE seems to be accurate when applied to micellar/polymer floods. Its appropriateness in high pH flood modeling is in question, however, and we hope to make insights into this issue in this paper also. paper also. UTCHEM also accounts for the reaction of a base with the acid in the crude oil to form in-situ generated surfactant, its lowering of interfacial tension, the resulting increase in capillary number, and the effects of this increase on relative permeability and residual phase saturations. Also, other significant property models, such as for phase behavior, polymer viscosity, and adsorption previously validated upon the micellar/polymer process, were used in our simulator without modification, process, were used in our simulator without modification, except for the inclusion of pH dependence. All of these models as well as the numerical solution scheme used in our simulator are given in complete detail in references 18 and 19.
This paper compares the published results of four experimental high-pH corefloods with the numerical results obtained by simulating these experiments using the augmented version of UTCHEM. The coreflood experiments are from the work of Shuler et al. The main reason for selecting these experiments are the relative completeness of the information on the materials used in these experiments, the experimental procedure, and analysis of the injected and the produced fluid compositions. The coreflood experiments referred to as B-AP-1, B-AP-2, B-AP-3 and B-MAP-2 in their paper are selected for this simulation study; the same nomenclature will be used here to refer to these experiments.
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