A New Method to Determine the Lower Limit of Reservoir Physical Properties—Corrected Minimum Flow Pore-Throat Radius Method
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E3S Web of Conferences 290, 03004 (2021) https://doi.org/10.1051/e3sconf/202129003004 ICGEC 2021 A New Method to Determine the Lower Limit of Reservoir Physical Properties—Corrected Minimum Flow Pore-throat Radius Method Jinyou Dai1,2,*, Lixin Lin2, and Rui Wang2 1State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum Beijing, Beijing, China 2School of Petroleum Engineering, China University of Petroleum Beijing, Beijing, China Abstract. The lower limit of reservoir physical properties is an important parameter for identifying reservoirs and determining effective thickness in reserves evaluation, and is also an important basis for selecting perforated test intervals in oilfield exploration and development. There are many methods to determine the lower limit of reservoir physical properties, and the minimum flow pore throat radius method is one of the commonly used methods. The method uses 0.1μm as the minimum flow pore-throat radius, and uses this to calibrate the lower limit of reservoir physical properties. However, according to the water film theory, the minimum radius of the reservoir's flowing pore throat is not a definite value, but varies with the displacement dynamics. Therefore, there is no exact basis for using 0.1μm as the minimum flow pore-throat radius, so it needs to be corrected. To this end, a new method for determining the lower limit of reservoir physical properties—the corrected minimum flow pore-throat radius method is proposed. The correction method comprehensively considers the factors of oil and gas accumulation dynamics, and determines the lower limit of reservoir physical properties by obtaining the minimum flow pore-throat radius value suitable for oil and gas accumulation dynamics. A case study of Chang 63 reservoir in A Oilfield shows that the minimum flow pore radius of oil and gas determined by the correction method is 0.08 μm, and the lower limit of reservoir physical properties (porosity 9.1%, permeability 0.117 × 10-3 μm2). The traditional method has a minimum flow pore-throat radius of 0.1 μm and a lower limit of reservoir physical properties (porosity of 9.8% and permeability of 0.133 × 10-3 μm2). Due to full consideration of the impact of oil and gas accumulation dynamics, the minimum flow pore-throat radius determined by the correction method is more reliable than the traditional method, and the lower limit of the reservoir physical property calibrated by it has practical significance. method is one of the commonly used methods to determine the lower limit of reservoir physical properties 1Introduction [24-31]. The method believes that the pores and throats of The lower limit of reservoir physical properties is the rocks are spaces and channels for oil and gas storage and minimum effective porosity and minimum permeability flow. Whether oil and gas can flow out of rocks under a that can store and percolate fluid. It is usually expressed certain pressure difference depends on the thickness of by a certain value of porosity or permeability [1]. The the throat. That is, the radius of the rock throat is the key lower limit of reservoir physical properties is an factor that determines whether oil and gas can flow out important parameter for identifying reservoirs and of the rock under a certain pressure difference. This determining effective thickness in reserves evaluation, minimum throat radius that can store oil and gas and allow oil and gas to seep is the minimum flow pore- and it is also an important basis for selecting perforated [24,25,32] test intervals in oilfield exploration and development [2-3]. throat radius of oil and gas . After determining the In view of the basicity and necessity of the lower limit of minimum flow pore-throat radius, the correlation curve reservoir physical properties, research on the lower limit of pore-throat radius and porosity and permeability can of reservoir physical properties is the focus of oil and gas be drawn according to the principle of statistical analysis, reservoir geology and engineering. For a long time, and the corresponding porosity and permeability lower limit values can be calibrated according to the minimum many scientists and technicians have conducted a lot of [26-27] research on the lower limit of reservoir physical flow pore-throat radius . At present, the minimum properties, and put forward more methods to determine flow pore-throat radius method generally adopts 0.1μm the lower limit of reservoir physical properties [4-31]. as the minimum flow pore-throat radius of oil and gas. It Among them, the minimum flow pore-throat radius is also believed that 0.1μm is equivalent to the thickness *Corresponding author e-mail: [email protected] © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). E3S Web of Conferences 290, 03004 (2021) https://doi.org/10.1051/e3sconf/202129003004 ICGEC 2021 of the water film attached to the surface of the water-wet limit, the displacement power is less than the seepage clastic rock. The pore-throat radius is less than this value. resistance, and the liquid does not flow. Therefore, the Oil and gas are not flowing, and the corresponding pore-throat radius in the displacement equilibrium state porosity and permeability values are the lower limits of is the minimum flow pore-throat radius. reservoir physical properties [24-31]. As the displacement power increases, the minimum The advantage of the minimum flow pore-throat flow pore-throat radius of the reservoir gradually radius method is that the lower limit of the reservoir decreases. When the minimum flow pore-throat radius of physical properties and the minimum flow pore-throat the reservoir is reduced to just the full use of oil and gas radius are linked together, and the lower limit of the in the reservoir, the corresponding minimum flow pore- reservoir physical properties corresponding to the throat radius is the minimum flow pore-throat radius of specific pore-throat radius (0.1μm) is calibrated. The the oil and gas, and the lower limit of physical properties process is simple and clear, easy to master. However, calibrated based on this is the effective lower limit. this method also has obvious shortcomings. The Because the production process is limited by many theoretical basis for determining the minimum flow pore- factors, it is difficult to accurately determine whether the throat radius as a fixed value (0.1 μm) is not sufficient. oil and gas are fully utilized and the minimum flow pore- According to previous studies on water film theory [33-34], throat radius when the oil and gas is fully utilized. the thickness of the water film attached to the rock However, considering that the process of oil and gas surface is not fixed, and the thickness of the water film is accumulation and production is the reciprocal process of a function of the displacement pressure. As the oil drainage and water flooding, the minimum flow pore- displacement power increases, the thickness of the water throat radius of oil and gas can be obtained according to film gradually decreases, and the corresponding the oil and gas accumulation dynamics. minimum flow pore-throat radius of oil and gas must The mercury intrusion curve is a curve reflecting the also decrease, which shows that the minimum flow pore- change of the saturation of the non-wet phase with the throat radius should not be a certain value. From this displacement pressure during the displacement of the point of view, it is not appropriate to use 0.1μm as the wet-phase fluid by the non-wet phase fluid. The mercury minimum flow pore-throat radius, and there is a certain intrusion process can be regarded as the accumulation deviation in the lower limit of the physical properties and filling process of oil drainage, so the mercury calibrated by this. Therefore, how to calculate the intrusion curve actually reflects the correspondence minimum flow pore-throat radius value more accurately? between oil saturation and accumulation dynamics. In It is the key to objectively calibrate the lower limit of other words, the mercury inlet pressure corresponding to reservoir physical properties using the minimum flow the original oil saturation read on the mercury pressure pore-throat radius method. To this end, this paper curve is the accumulation power, and the pore-throat proposes a new method to determine the lower limit of radius corresponding to this accumulation power is the reservoir physical properties-the corrected minimum minimum pore-throat radius of oil and gas. Based on the flow pore-throat radius method (hereinafter referred to as determination of the minimum flow pore-throat radius, the correction method). and then based on the principle of statistical analysis, the correlation curve of pore-throat radius and porosity and permeability is drawn, and the lower limit of reservoir 2 Method principle physical properties can be calibrated according to the Pore throats in reservoirs vary in size and geometry, and minimum flow pore-throat radius. Taking the Chang 63 pore throats of different orders interweave to form an reservoir in the A oilfield of the Ordos Basin as an intricately interconnected system. The complexity of the example, the lower limit of the physical properties of the reservoir pore-throat network, especially the order of reservoir is determined by the correction method. pore-throat distribution, will inevitably have a direct and significant effect on the seepage response of the reservoir 3 Calculation example fluid. When the displacement power is constant, only the part of the pore-throat network with pore-throat size greater than a certain limit will seep, while other parts of 3.1 Geological overview the pore-throat network below this limit cannot seep.