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.
Sodium bisulfite (SBS) oxygen scavenger is being applied in several sea water flood injection systems in the Gulf of Mexico. High corrosion rates (CRs) were observed in one particular field during periods when oxygen scavenger injection rates were elevated. In an effort to establish a safe operating concentration for oxygen scavenger, testing was conducted over a range of conditions to determine the corrosivity of the oxygen scavenger in seawater. Initial test work identified corrosion rate spikes upon injection of SBS in the laboratory and all subsequent work was designed to determine the mechanism generating these corrosion spikes. Scavenger performance was studied with and without the presence of oxygen. Parameters included in this study were SBS concentration, tetrakis-hydroxymethyl-phosphonium (THPS) concentration, temperature, and pH. Electrolyte simulation software was used to determine the dominant aqueous reactions that may contribute to the corrosive environment. This paper outlines the test protocols and results of the lab tests as well as the aqueous modeling. According to the test results and aqueous simulations, the field dose rate of 49 ppm SBS appears to be safe with respect to corrosivity and effective at eliminating the dissolved oxygen.
Seawater injection is critical to many offshore Gulf of Mexico assets as it directly correlates to oil production.1 For the asset of interest, the topsides process used to treat seawater for injection has had an increase in piping failures over the last two years. The operator investigated the root cause of the pipe failures and develop an action plan to eliminate or significantly decrease the effects of any identified corrosion mechanism. It was concluded that the increase in failures may have resulted from more than one corrosion mechanism, and oxygen control was identified as a key factor in managing the integrity of the seawater processing system. Currently, oxygen scavenger injection is the sole technique for oxygen corrosion mitigation. The oxygen scavenger chemistry is catalyzed sodium bisulfite. The asset contains yellow metals and therefore ammonium bisulfite is excluded from use on this platform.
The investigation uncovered a correlation between elevated oxygen scavenger concentrations and increased corrosion rates. The operator devised an initial lab test plan to determine the impact of the current oxygen scavenger, SBS-35 (SBS at 35wt% concentration), on corrosion rate. Based on the system conditions of low temperature and low shear the rotating cylinder electrode (RCE) was selected as the test method of choice. After a joint-effort between the operator and Baker Hughes on reviewing and discussing the test results, a total of four rounds of test sets were performed to study the impacts of various parameters on corrosion. The test design is summarized as follows:
Yang, Kun (PetroChina XOC) | Du, Hongling (PetroChina XOC) | Zhang, Yi (PetroChina XOC) | Huang, Lei (PetroChina XOC) | Zeng, Yanqiang (PetroChina XOC) | Wu, Congwen (PetroChina XOC) | Lin, Xin (Schlumberger) | Kok, Jeffrey (Schlumberger) | Wang, Dahai (Schlumberger) | Wang, Yong (Schlumberger) | Koon, Lee Tow (Schlumberger)
Luliang oilfield has been in production since 2001 and was originally developed from vertical wells. To arrest production decline, operators embarked on a horizontal drilling campaign in 2006 to achieve ultimate field recovery from remaining oil. A proper geosolution to optimize reservoir exposure while maximizing distance from bottom and edge-water was recognized as the key for success in this field.
From 2006 to 2015, the 10 years of field development was sustained through a close collaboration between the operator and service provider. However, production reviews indicate that the Luliang oilfield is approaching the end of its field life as the main underground reserve is drained away. As this mature oilfield becomes increasingly difficult to develop, well placement technologies become increasingly critical along with the commitment to service quality. With the challenge increasing, the well placement strategy and solutions must be reformed as well. Innovative use of well placement technology and workflows are crucial to ensure service quality while balancing drilling costs within the margin of economics.
From 2006 to 2014, a total of 200 horizontal wells were successfully constructed, achieving net-to-gross over 94% and improving the field's recovery efficiency by over 96%. Both productivity and cumulative production of horizontal wells were significantly enhanced compared to the original objectives. In 2015, 14 horizontal wells are on going; thus, after 10 years, the extension of this mature field's vitality continuous to press on.
Localized corrosion of carbon steel welds has been thought to arise primarily from galvanic effects due to compositional differences between the deposited weld metal, the parent steel, and the heat affected zone induced by the welding process. The location and morphology of the preferential corrosion is influenced by a complex interaction of environmental parameters.
The effects of salt concentration and temperature on intrinsic and galvanic corrosion of the non-alloyed standard carbon steel weldment in CO2 environments have been investigated using different types of electrochemical techniques. Experimental results show that for the non-alloyed standard weldment, the intrinsic corrosion rates of parent metal, heat affected zone (HAZ) and weld metal are not significantly different, but the corrosion of weld metal becomes worse and the parent metal is protected due to the galvanic effects between the segments. The experimental results also show that an increase of salt concentration (1-10 wt.% NaC1) significantly affected the intrinsic corrosion rate in a nonlinear fashion. The galvanic currents were unaffected by the different salt concentrations.
Based on high pressure physical property experiments, such as swelling experiment, multi-contact experiment and asphaltene precipitation experiment et al, thermodynamic characteristics of asphaltene precipitation during CO2 injection have been analyzed comprehensively with numerical simulation, which make up the deficiency of analyzing physical and chemical parameters with experiments; adsorption and plugging of asphaltene on rocks and rheology characteristic of oil containing precipitated asphaltene have been studied; the influence of asphaltene deposition on reservoir have been researched; Found on above-mentioned study, the mathematic flow model considering asphaltene deposition has been established. Take one oil field in our country as example, the influence of asphaltene deposition on production dynamics during CO2 injection has been researched. The results were in agreement with field observation and history data, which can be efficient for the further production prediction.
Gas injection, especially CO2 injection, is regarded as one of the most efficient methods of oil development because CO2 can obviously enhance oil recovery by decreasing viscosity of crude oil, reducing interfacial tension, and swelling oil. However, CO2 injection, steam injection and N2 injection etc. may cause asphaltene deposit, which seriously influences production. Oil production indicates that gas injection can easily trigger heavy organic matters deposit, which can result in plugging of the formation, wellbore and production facilities. Many domestic and oversea oil fields have reported this phenomenon. Thus, it is necessary to propose a predictive model to describe asphaltene physical chemisty property, exactly predict asphaltene precipitation and quantify the influence of asphaltene deposition on oil development.
In this paper, through the investigation of comprehensive literatures, first of all, multiphase equilibrium thermodynamic model for asphaltic oil gas system is proposed based on the theory of fluid thermodynamics; and then, taken example for some case reservoir fluid in China, asphaltene precipitation values are calculated, and the variation trends of thermodynamic parameters of alphaltene with injected CO2 are analyzed; Next, based on the phase behavior characteristic research of asphaltic oil, compositional model considering asphaltene deposition, adsorption, plugging and non-Newton characteristic under low pressure gradient during gas injection is proposed; Subsequently, long core flooding experiment is simulated in order to discuss dynamic characteristic of asphaltene deposition, distribution rules of asphaltene deposition and adsorption, and receptance factors of asphaltene deposition. Finally, single injection and single production model is constructed to research the influence of oil rheological property and asphaltene deposition and adsorption on oil recovery.
Multiplashe Equilibrium Research on Asphatic Oil System during CO2 Injection
Organic solid precipitation during gas injection is complicated physical chemistry process induced by phase transition in oil and gas system. However, even though a lot of experiments and theory researches have been conducted since the sixties of the twentieth century, the true mechanism of asphaltene precipitation in oil system is not explored clearly.
Especially, during CO2 injection, phase behavior characteristic is very intricate. The contact of injected CO2 and formation oil may induce multiple phase coexistence. However, only equipments with very high precision can distinguish multiple phase characteristic such as two liquid phases. In addition, because precipitated asphaltene is black or dark brown and opaque, which is not be clearly identified with the interphase between asphaltene and oil, the equipments can not accurately determine asphaltene precipitation onset point and asphaltene precipitation quantity.
Thus, it is necessary to propose multiphase equilibrium thermodynamic model for asphaltic oil and CO2 system to research on the asphaltene precipitation. With this model, thermodynamic characteristics of asphaltene precipitation during CO2 injection can be analyzed comprehensively, which may make up the deficiency of analyzing physical and chemical parameters with experiments.