Jia, Ying (Petroleum Exploration and Production Research Institute, SINOPEC) | Shi, Yunqing (Petroleum Exploration and Production Research Institute, SINOPEC) | Huang, Lei (Research Institute of Petroleum Exploration and Development, Petrochina) | Yan, Jin (Petroleum Exploration and Production Research Institute, SINOPEC) | Sun, Lei (SouthWest Petroleum University)
The YKL condensate gas reservoir is one of the biggest condensate gas reservoirs in China and has been developed more than 10years. At present, the combination of subdivision layer, production speed optimization and horizontal well drilling has been the key to economically unlocking the vast reserves of the YKL condensate gas. The primary recovery factor, however, remains rather low due to high capillary trapping and water invasion. While primary depletion could result in low gas recovery, CO2 flooding provides a promising option for increasing the recovery factor.
The objective of this work is to verify and evaluate the effect supercritical CO2 on enhancing gas recovery and analyze the feasibility of CO2 enhance gas recovery (CO2 EGR) of condensate gas reservoir.
Firstly, novel phase behavior experimental procedures and phase equilibrium evaluation methodology for gas-condensate phase system mixed with supercritical CO2 with high temperature were presented. A unique phase behavior phenomena was also reported. Then, CO2 floodingmechanism in condensate gas reservoir was analyzed and clarified based on experiments. Finally, a series of numerical simulation work were conducted as an effective and economical means to maximize natural gas recovery with the lowest CO2 breakthrough by varying strategies, including CO2 injection rate, injection composition, andinjection timing. Meanwhile the CO2 storage volumes of different strategies were calculated.
The results show that higher gas recovery factor can be achieved with CO2 injection through appearing interphase between two fluids, maintaining reservoir pressure, driving gas like "cushion" and controlling water invasion. All strategies have moderate to significant effects on gas production. The control of injection and production ratio needs to be balanced between pressure transient and CO2 breakthrough over the producer to obtain the maximum gas production. The varying injection pressure shows a positive effect of enhancing gas production. Numerical simulation indicated that the recovery of gas reservoir was improved by around 10 percent. The total CO2 storage would be around 30-40% HCPV.
The research showed that CO2 flooding presents a technically promising method for recovering the vast condensate gas while extensively reducing greenhouse gas emissions.
Wang, Keke (SouthWest Petroleum University) | Peng, Xiaolong (SouthWest Petroleum University) | Du, Zhimin (SouthWest Petroleum University) | Haghighi, Manicher (Zhenjiang You) | Yu, Lu (Notheast Sichuan Gas production plant, Southwest Branch company, Sinopec Corporation)
In traditional Discrete Fracture Network (DFN) method for fractured porous media simulation, fractures are modelled in different scales and orientations using single computational grid. However, a large number of small grids near both ends of fracture are generated, which substantially reduce the computation efficiency. In this paper, a new line fracture approach is presented to avoid generation of small grids. Combined with Multi-Point Flux Approximation (MPFA) algorithm, the simulation efficiency is highly improved without losing accuracy.
We present a modified mesh generation algorithm in which the volume of large fractures is set zero by neglecting the fracture width. The fracture aperture (very short line) is treated as single node during mesh generation using the paving method. Therefore, the number of small grids around the fracture is significantly decreased. In this paper, a quadrilateral unstructured grid system is generated using the proposed paving method. Then, by taking the median dual of quadrilateral mesh as the control volume, all fracture properties such as the aperture and permeability are accounted for as independent parameters in discrete fractures. The governing equations of DFN model are derived and solved using MPFA algorithm for oil-water two-phase flow.
A new discrete fracture network model using line fracture approach is developed. To show the efficiency and accuracy of the new model, the proposed method is applied to a case study of two separated and two crossed fractures, in the computation domain with the scale of 50 by 50 meters. Compared with the standard DFN model including the width of fractures, the computation efficiency of the new model is highly improved (by 2.5 times), due to the large reduction of grid numbers (20%). Good agreement in water and oil saturation distributions resulted from the two models validates the newly developed method.
Simulation of naturally fractured reservoirs has been a challenge for decades. Discrete fracture network modelling is a promising approach. However, without an efficient grid generation method, DFN model is not feasible and practical due to the large amount of computational time. The novelty of the present work is the improved model using line fracture approach. The new grid generation algorithm is coupled with multi-point flux approximation approach for flow simulation in fracture network system. High efficiency and accuracy of the developed method is readily applied to fractured reservoir simulation.
Sponsored by NSFC (Natural Science Fund of China - "the numerical simulation of natural fractured reservoir based on the unstructured hexahedral grid system and concurrent computation") (No. 51474179)
One of the most common methods to prevent scale deposition in the near wellbore area is through the application of squeeze treatments which conventionally consist of pre-flush, main treatment, overflush, shut-in and back production stages. The use of additives such as polyamino acids and polyquaternary amines has often been successfully applied as part of the pre-flush stage of squeeze treatments to improve treatment lifetimes (
A new sand pack methodology which provides a better simulation of field squeeze treatments than traditional corefloods has been designed to provide a better understanding of the scale inhibitor retention mechanisms when polyquaternary amines are applied in pre-flush treatments. This has enabled improved treatment modelling and the impact of these additives to be understood in field treatments.
The performance of the polyquaternary amine is dependent upon scale inhibitor chemistry and the mechanisms of retention are addressed for both polymeric and phosphonate scale inhibitors. The adsorption isotherms were derived and compared in the absence/presence of the polyquaternary amine using specialized software, and applied to predict squeeze lifetime in field scenarios.
This paper provides an understanding on the effects of polyquaternary amines on squeeze lifetime for both phosphonate and polymeric scale inhibitors supported by the application of a newly developed test methodology and computer modelling techniques. In addition, the combination of laboratory and computer modelling data coupled with field experience and a better understanding of the retention mechanisms involved now provides the ability to improve and optimize field squeeze treatment designs with polyquaternary amine pre-flush additives.