RU1480411C - Method for development of oil bed - Google Patents

Abstract

FIELD: oil-producing industry. SUBSTANCE: volume of bed zones to be plugged with gypsum in the area of inhomogeneous terrigenous bed is determined by geophysical and hydrodynamic surveys. For this purpose certain amounts of aqueous suspension of calcium carbonate, concentration 10-55 wt.-% and 80-86% sulfuric acid separated with a liquid inert to both reagents (diesel fuel or distillate) are injected in succession with sulfuric acid fringe into the bed in the amount of 1-5% of sulfuric acid volume. The volumes of calcium carbonate ((kg/m³)) and sulfuric acid (m³) are calculated by the formulas submitted in the description of the invention. EFFECT: higher efficiency of bed development achieved by increased flooding. 2 cl, 3 tbl

Description

 The invention relates to the oil industry, in particular to increasing oil recovery of heterogeneous permeability waterfloods, oil-water zones of oil deposits, as well as fields with high initial water saturation.

 The aim of the invention is to increase the efficiency of development by increasing the coverage of the formation by water flooding.

The method is as follows. A complex of geophysical and hydrodynamic studies is carried out on a selected area of a heterogeneous terrigenous formation drilled by at least two wells, one of which is injection and the other is producing, based on which the volume of formation zones that must be plugged with gypsum (V _g ) is determined, and their remoteness from the injection well. Calculate the amount of reagents that need to be injected into the reservoir. A suspension of calcium carbonate is prepared. To do this, dry calcium carbonate is fed into a mixing tank, into which the calculated amount of water from a water conduit or tank truck of type 4CR is added and the mixture is mixed until a homogeneous suspension.

·10² (1)
V_к=

10²+(0,005-0,01)·V_пор (2) где V_г - обьем гипса, м³;
С_с, С_к, d_c, d_к - соответственно концентрации (мас.%) и плотности (кг/м³) суспензии карбоната кальция и серной кислоты;
V_пор - объем пор обрабатываемого пласта, м³.The prepared suspension is pumped into the injection well (for example, type AN-700), and then the rim of the liquid inert to calcium carbonate and sulfuric acid (for example, diesel fuel or distillate), after which the rim of sulfuric acid is pumped. The volume of suspension of calcium carbonate (V _c ) and sulfuric acid (V _to ) is calculated by the following formulas:
V _c =

10 ² (1)
V _to =

10 ² + (0,005-0,01) · V _then (2) where V _g - volume of gypsum, m ³ ;
C _s , C _k , d _c , d _k - respectively, the concentration (wt.%) And density (kg / m ³ ) of a suspension of calcium carbonate and sulfuric acid;
V _then - the pore volume of the treated formation, m ³ .

 The first term of equation (2) determines the amount of sulfuric acid needed to convert calcium carbonate to gypsum, i.e. this part of the acid goes to block the highly permeable washed part of the reservoir. The second term of equation (2) determines the amount of acid needed to improve the oil washing properties of water according to the prototype.

 Suspension of calcium carbonate enters mainly in highly permeable, water-washed zones in which particles of calcium carbonate settle. A hint of sulfuric acid is sent to the same areas where an interaction reaction occurs between calcium carbonate, sulfuric acid and water, which results in the formation of gypsum and carbon dioxide. Gypsum clogs high-permeability zones, as a result of which the following portions of sulfuric acid are sent to low-permeability zones. When gypsum is formed, water also binds (2 water molecules per 1 calcium sulfate molecule), which reduces water saturation in the sulfuric acid exposure zone, resulting in an increase in the effectiveness of sulfuric acid.

 The effectiveness of the proposed method in comparison with the known tested in laboratory conditions on the models of the reservoir.

The test used calcium carbonate with a particle size of 4-28 microns. Suspensions of certain concentrations were prepared by adding water to a sample of calcium carbonate and mixing until a homogeneous, lump-free mass was obtained. As sulfuric acid used alkylated sulfuric acid (ASA), which is a waste of the process of alkylation of hydrocarbons by the butane-butylene fraction. The waste contains up to 86% sulfuric acid, 4-10% sulfonic acids, 6-8% resinous substances and up to 6% water. Prior to the experiments, an ASA containing 80% sulfuric acid with a density of 1600 kg / m ^{3 was used} . The buffer fluid was diesel fuel. Devonian oil with a density of 0.842 g / cm ³ and a viscosity of 5.0 MPa ˙ s was used as oil.

 The experiments were carried out on artificial reservoir models representing a system of elements (glass tubes 30 cm long, 2 cm in diameter, filled with quartz sand). Each model consisted of two elements, one of which had a permeability 10 times higher than the other, which was achieved by selecting the appropriate sand fractions.

 The porous medium of each element individually was saturated with oil, then the elements were combined into a model so that it had one common entrance and separate exits from each element. Oil was displaced from each model by water to a water cut of 98-99% at the outlet of the element with high permeability.

At the input of one model, a rim of a SC with a volume of 0.01% of the pore volume of the model was applied (known method). The edges of a suspension of calcium carbonate, diesel fuel and ASA (the described method) were successively fed to the input of the second model. The concentration of calcium carbonate in the suspension was changed from 10 to 55 wt. % The volumes of the rims of the suspension and ASA were calculated by the formulas (1) and (2). The volume of the rim of diesel fuel was 0.1 cm ³ . Then, three pore volumes of water were pumped through both models.

100
K″=

100
Δ К = К'' - К' где К' и К'' - первичный и конечный коэффициенты вытеснения, %;
V_о - начальный объем нефти в пористой среде, см³;
V₁ - объем нефти, вытесненной первично водой, см³;
V₂ - объем нефти, вытесненной при доотмывке оторочкой химреагентов и водой, см³;
Δ К - прирост коэффициента вытеснения, %.Processing the experimental results was carried out according to the following formulas:
K ′ =

100
K ″ =

100
Δ K = K '' - K 'where K' and K '' are the primary and final displacement factors,%;
V _about - the initial volume of oil in a porous medium, cm ³ ;
V ₁ - the volume of oil displaced primarily by water, cm ³ ;
V ₂ - the volume of oil displaced during washing with a rim of chemicals and water, cm ³ ;
Δ K is the growth rate of displacement,%.

 The results of the experiments are given in table. 1.

 From the data table. Figure 1 shows that as a result of the injection of the rim of the calcium carbonate suspension before the ASK rim, the displacement coefficient from the low-permeability element substantially increases (on average, 10 times), and in the model as a whole this increase is 8.9% compared to the known method.

 The lower limit of the concentration of the suspension is determined by the fact that the injection of less concentrated suspensions leads to a significant dilution of sulfuric acid with water. The upper limit is limited by the high viscosity of the suspension and, accordingly, the complexity of the process of pumping it.

 The results are shown in table. 2.

 Experiments were also conducted to determine the effect of inert fluid rims on the depth of the formation. The experiments were carried out on reservoir models, which were glass tubes with a diameter of 1 cm, a length of 50 cm with one input and one output. The porous medium of the models was saturated with water and the rims of a 25% suspension of calcium carbonate, diesel fuel, and ASA were pumped through them sequentially. The sizes of the suspension rims and ASA in each experiment remained constant, and the size of the diesel rims varied. Outlines were pushed according to the model with one pore volume of water. Then, the distance from the model inlet to the zone of gypsum sedimentation was measured by extracting successively portions of the bulk porous medium from the model and its chemical analysis on the gypsum.

 The results are shown in table. 3.

 The presence of an inert liquid between the rims of the suspension and sulfuric acid moves the precipitation zone away from the injection site of the reagents, and the remoteness of this zone depends on the size of the inert liquid rim.

Claims (2)

 1. METHOD FOR DEVELOPMENT OF THE OIL LAYER, including the injection of rim of sulfuric acid into the formation through injection wells with water and its selection through production wells, characterized in that, in order to increase development efficiency by increasing the coverage of the formation by water flooding, before the sulfur rim acid in the reservoir is sequentially injected with an aqueous suspension of calcium carbonate concentration of 10 to 55 wt.% and a fluid inert to calcium carbonate and sulfuric acid in a volume of 1 to 5% of the volume of sulfuric acid.  2. The method according to claim 1, characterized in that, as a liquid inert to calcium carbonate and sulfuric acid, diesel fuel or distillate is used.

Images