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Ocena możliwości zrzutu zasolonych wód poeksploatacyjnych do wyeksploatowanych odwiertów

Budak Paweł, Szpunar Tadeusz

Nafta-Gaz

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2021

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R. 77, nr 11

752--759

PL

W artykule omówiono zagadnienia zrzutu zasolonych wód poeksploatacyjnych do porowatych warstw chłonnych o niskim ciśnieniu złożowym – z zastosowaniem pompy lub bez niej. Podano warunki, jakie musi spełniać warstwa chłonna, oraz klasyfikację odwiertów zrzutowych według amerykańskiej Agencji Ochrony Środowiska (EPA) ze względu na ochronę wód pitnych. Zasygnalizowano, jakie warunki musi spełniać solanka wprowadzana do ośrodka porowatego, w tym dotyczące jej składu chemicznego, zawartości ciał stałych, obecności bakterii oraz zawartości olejów i tłuszczów. Podano sposoby określenia przepuszczalności warstwy o niskim ciśnieniu złożowym, z której brak jest samoczynnego wypływu i lustro cieczy stabilizuje się na pewnej głębokości poniżej poziomu terenu, w tym omówiono metodę tzw. slug test oraz metodę INiG – PIB opracowaną przez autorów. Podano warunki techniczne, których spełnienie wymagane jest do prawidłowego przeprowadzenia slug testu. Omówiono wady i zalety poszczególnych metod określania przepuszczalności w odwiertach, w których nie ma produkcji samoczynnej, oraz sposoby interpretacji wyników, jak również podkreślono prostotę interpretacji metodą INiG – PIB w porównaniu z metodą slug testu, wymagającą wpasowania krzywych pomiarowych do krzywych teoretycznych. Podano sposób przybliżonej oceny objętości wody zasolonej, którą można wprowadzić do otworu „na chłonność”, to jest bez użycia pompy, przy maksymalnym ciśnieniu hydrostatycznym odpowiadającym wypełnieniu otworu solanką „do wierzchu”, oraz objętości, którą można wtłoczyć za pomocą pompy przy ciśnieniu niższym od ciśnienia szczelinowania warstwy porowatej. Podano przykład obliczeniowy.

EN

Discussed are the problems related to salt water discharge into low pressure porous rocks, with or without an injection pump. Specified are conditions which the porous rock should satisfy to be classified as an injection one. The American Environmental Protection Agency (EPA) classification of injection wells is given as well as regulations regarding protection of drinking water sources. Considered are low pressure wells which do not flow to the surface i.e. in which the water table stabilizes at some depth below the ground level. It is assumed that the full column hydrostatic pressure is used to force the salt water flow into porous rock. Provided are parameters which make the salt water suitable for injection. Provided are the regulations regarding its chemical composition, solids content, presence of bacteria and oil/grease content which the salt water should meet. Discussed are the methods for evaluation of permeability of porous rocks in wells with reservoir pressure lower than the pressure exerted by the full column of salt water. Included here are slug test method and INiG – PIB method which are routinely used for evaluation of permeability of low pressure porous zones. Discussed are advantages and disadvantages of each method and analyzed are the testing procedures related to each of them. Presented is the technique for approximate evaluation of salt water volume which can be introduced into porous rock without using the injection pump and salt water volume which can be injected at pressures lower than the fracturing pressure of porous rock. Presented are the example calculations.

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Improved numerical inverse Laplace transformation to improve the accuracy of type curve for analyzing well testing data

Kim Song Chol, Song Yong Il, Han Chol Gwang

Acta Geophysica

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2021

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Vol. 69, no. 3

919--930

EN

Analyzing well-testing data by the type-curve matching is a modern well-testing analysis method and is widely used in the petroleum and gas industry. By improving accuracy of type curve, we can get more accurate results from analyzing welltesting data, which provide a scientifc base for development of oil, gas and water resources. By solving percolation equations, we can obtain type curves. The Laplace transformation methods are often used to solve them. In this paper, we improve the accuracy of type curve by improving the numerical inverse Laplace transformation (NILT) based on infinite series. We combine the NILT based on infinite series with Levin convergence acceleration and determine necessary parameters through numerical experiments to improve accuracy and speed. To verify this method, we compare the improved method with the Stehfest method using some functions such as trigonometric function. Type curves for analysis of well-testing data for the homogeneous reservoir with elastic outer boundary and a dual porosity reservoir are plotted and compared by using the improved numerical inversion and the Stehfest numerical inversion, respectively. These results show that type curves plotted by the improved method are less in vibration and fuctuation than ones plotted by the Stehfest method.

3

Analyzing fuid fow characteristics in a dual porosity reservoir with an elastic outer boundary

Kim Song Chol, Han Chol Gwang, Rim Myong Won, Kim Ju Song, Ryang Myong Jun

Acta Geophysica

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2021

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Vol. 69, no. 5

1843--1853

EN

When we develop petroleum and natural gas reservoirs, we can see a lot of dual-porosity reservoirs with both pores and fractures. Many researchers have studied characteristics of fluid flow in dual-porosity reservoirs with the ideal outer boundary (infinite boundary, closed boundary or constant pressure boundary) but nobody has considered dual-porosity model with the elastic outer boundary (EOB) reflecting the real condition. So there could be large errors in analyzing well-test data for dual-porosity model. In this paper, we establish a percolation model for dual-porosity reservoirs with the EOB and consider the skin factor and wellbore storage. And we obtain its solution in Laplace space by introducing the effective well radius and applying the Laplace transformation. An approximation in Laplace space is also derived by using an asymptotic formula of I0(x) and I1(x). By using Stehfest numerical inversion of Laplace transformation, the solution in the real space is obtained. We compare this model to homogeneous model with the EOB and conventional dual-porosity model, respectively. Comparison results show that the conventional outer boundary conditions are three special cases of the EOB and homogeneous model with the EOB is a special case of dual-porosity model with the EOB. Flow characteristics are analyzed and it is shown that the EOB affects analysis of well-test data through simulation. This study may improve the accuracy of well-test analysis for dual-porosity reservoir.

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Unsteady inter-porosity flow modeling for a multiple media reservoir

Nie R.-S., Meng Y.-F., Jia Y.-L., Shang J.-L., Wang Y.

Acta Geophysica

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2012

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Vol. 60, no. 1

232-259

EN

The paper deals with unsteady inter-porosity flow modeling of underground fluid in a multiple media reservoir. Assuming spherical vugs, symmetrically distributed pressure, negligible inter-porosity flow between matrix and vug systems and centrifugal flow of the fluid from matrix blocks or vugs to fractures, and treating media directly connected with wellbore as the fracture system, we establish and solve a model of unsteady inter-porosity flow for dual and triple porosity media reservoirs. We provide simulated graphs of pressure and pressure derivative log-log type curves, and analyze the transient flow process and characteristics of type curves affected by different parameters. The new type curves of unsteady inter-porosity flow modeling are evidently different in shape and characteristics from those of pseudo-steady inter-porosity flow modeling. The location of dimensionless pressure of unsteady inter-porosity is lower than that of pseudo-steady inter-porosity, which indicates that unsteady inter-porosity flow accelerates an energy supplement during production. Qualitatively, the unsteady inter-porosity flow modeling reduces the classical V-shaped response. We also estimated parameters from well test data in real applications using this model.