Numerical Simulation of Asphaltene Precipitation and Deposition during Natural Gas and CO_(2) Injection

Asphaltene deposition is a significant problem during gas injection processes,as it can block the porous medium,the wellbore,and the involved facilities,significantly impacting reservoir productivity and ultimate oil recovery.Only a few studies have investigated the numerical modeling of this potential effect in porous media.This study focuses on asphaltene deposition due to natural gas and CO_(2) injection.Predictions of the effect of gas injection on asphaltene deposition behavior have been made using a 3D numerical simulation model.The results indicate that the injection of natural gas exacerbates asphaltene deposition,leading to a significant reduction in permeability near the injection well and throughout the reservoir.This reduction in permeability strongly affects the ability of gas toflow through the reservoir,resulting in an improvement of the displacement front.The displacement effi-ciency of the injection gas process increases by up to 1.40%when gas is injected at 5500 psi,compared to the scenario where the asphaltene model is not considered.CO_(2) injection leads to a miscible process with crude oil,extracting light and intermediate components,which intensifies asphaltene precipitation and increases the viscosity of the remaining crude oil,ultimately reducing the recovery rate.

CO_(2)驱分层注气工艺管柱适用性分析及展望

目前,我国现场应用的注气管柱多为笼统注气管柱、同心双管分层注气管柱及偏心投捞分层注气管柱,该类管柱存在着分层数受限、测调效率低、测调精度差及适应性差等问题,难以满足CO_(2)驱油田的精细、高效开发需求。针对这一现象,在现有成熟分层注水管柱的基础上,设计了液控分层注气管柱、测调一体分层注气管柱、有缆智能分层注气管柱,并对这3种分层注气管柱进行了技术适应性分析和实施难点分析,分析发现:所设计的3种分层注气管柱各有优势,配套井下气体流量计的研制既是设计管柱的主要实施难点也是实现精细化注气的关键。最后,对各类流量测量技术进行了技术特性及研究难度分析,并对井下气体流量计的设计选型提出了建议和展望。

Experimental Investigation on Condensate Revaporization During Gas Injection Development in Fractured Gas Condensate Reservoirs

The gas field in the Bohai Bay Basin is a fractured metamorphic buried-hill reservoir with dual-media characteristics. The retrograde vaporization mechanism observed in this type of gas condensate reservoir differs significantly from that observed in sand gas condensate reservoirs. However, studies on improving the recovery of fractured gas condensate reservoirs are limited;thus, the impact of retrograde vaporization on condensate within fractured metamorphic buried-hill reservoirs remains unclear. To address this gap, a series of gas injection experiments are conducted in pressure-volume-temperature(PVT) cells and long-cores to investigate the retrograde vaporization effect of condensate using different gas injection media in fractured gas condensate reservoirs. We analyze the variation in condensate volume, gas-to-oil ratio, and condensate recovery during gas injection and examine the influence of various gas injection media(CO_(2), N_(2), and dry gas) under different reservoir properties and varying gas injection times. The results demonstrate that the exchange of components between injected gas and condensate significantly influences condensate retrograde vaporization in the formation. Compared with dry gas injection and N_(2) injection,CO_(2) injection exhibits a superior retrograde vaporization effect. At a CO_(2) injection volume of 1 PV, the percentage shrinkage volume of condensate is 13.82%. Additionally, at the maximum retrograde condensation pressure, CO_(2) injection can increase the recovery of condensate by 22.4%. However, the condensate recovery is notably lower in fractured gas condensate reservoirs than in homogeneous reservoirs, owing to the creation of dominant gas channeling by fractures, which leads to decreased condensate recovery. Regarding gas injection timing, the effect of gas injection at reservoir pressure on improving condensate recovery is superior to that of gas injection at the maximum retrograde condensation pressure. This research provides valuable guidance for designing gas injection development plans and dynamic tracking adjustments for fractured gas condensate reservoirs.

CO_(2)驱注入管柱温度压力耦合模型建立及其敏感性因素研究

为了准确分析CO_(2)驱注入管柱的受力情况,需要考虑CO_(2)流体在注入管柱内的相态分布,合理预测CO_(2)驱注入管柱温度场、压力场分布。首先,根据三大守恒定律建立了CO_(2)驱注入管柱温度压力及物性参数耦合微分方程;然后,根据四阶龙格库塔算法的计算步骤编制MATLAB程序分析某油田4口CO_(2)驱注入管柱的温度场与压力场;最后,对CO_(2)驱注入管柱的温度场、压力场分布进行了敏感性因素分析。结果表明:在CO_(2)驱注入的过程中,CO_(2)驱注入管柱的温度和压力均随地层深度的增加呈近似线性增长,流体温度在管柱1 400 m之后均超过临界温度(31.1℃),CO_(2)流体相态转变为超临界态;注入管柱温度场分布受CO_(2)流体注入速度影响最为显著,其敏感度系数达到3.10;注入管柱压力场分布受CO_(2)流体注入压力影响最为显著,其敏感度系数达到6.00。

苏北油田CO_(2)驱油同心双管分层注气技术

为了解决苏北油田CO_(2)驱油常规笼统注气工艺在实际应用中存在的吸气剖面不均匀、高渗层气窜严重和低渗层动用程度低等问题,在分析常规分层注气工艺特点的基础上,通过设计双级锚定式管柱、优选防腐蚀材质和质量流量计、改进分注器等井下工具,形成了CO_(2)驱油同心双管分层注气技术。根据现场实际情况,研究解决了管柱失稳、封隔器失效等问题,实现了准确分层注气。该技术在草舍油田C1井进行了现场试验,利用地面装置调节分层注入量,各项指标均满足分层配注要求,取得了良好的现场应用效果。试验结果表明,该技术具有操作简单、可靠性高和调配精度高等优点,可有效实现精细注气,为苏北油田CO_(2)驱油有效开发提供了新的技术手段。

注CO_(2)驱注入参数设计及井筒管柱应力变化规律研究

注CO_(2)驱油是提高油田采油率的三次采油重要技术手段,但对于超低渗储层CO_(2)驱管柱应力变化规律的研究较少。以HH156井数据为基础,结合超低渗油藏储层基本特征,确定了合理的CO_(2)每日注入量,井口最大注入压力,注入井井筒油管管柱。利用LandMark软件受力分析模块,通过对井筒油管管柱内压分布、轴向载荷分布、等效应力分布、变形及安全系数等分析,得出井筒油管管柱应力变化完全满足CO_(2)驱注入施工要求。为低渗透油藏注CO_(2)驱的开发和技术方案的编制提供重要的参考。

Assessing roles of geochemical reactions on CO_(2)plume,injectivity and residual trapping

With increasing CO_(2)concentration in the atmosphere,CO_(2)geo-aequestration has become a popular technique to counter the dangers of global warming resulting from high levels of CO_(2)in the atmosphere.This paper examins sequestration parameters such as CO_(2)plume behaviour,residual gas trapping and injectivity as a means of achieving safe and successful CO_(2)storage in saline aquifers.Mineral precipitation/dissolution rates are used to establish a relationship between these parameters and geochemical reactions in saline aquifers.To achieve this,mechanistic models(6 models with different inputs,created using CMG e GEM,2016 and WINPROP,2016)are simulated using input data from literature and studying changes in fluids and formation properties as well as mineral precipitation/dissolution rates in aquifers when subjected to different conditions in the different models.The results from the models show that high CO_(2)dissolution,which creates large CO_(2)plume,leads to high mineral dissolution/precipitation as results of increased fluid-rock interactions(geochemical reactions);whereas injectivity,although enhanced by CO_(2)-water cyclic injection,does not show much increase in bottom hole pressure when mineral trapping(thus geochemical reactions)is introduced into the model.Sensitivity study on residual gas trapping shows that high residual gas saturation leads to reduced mineral precipitation/dissolution due to the reduced amount of dissolved CO_(2)in brine.Also,rapid changes in the bottom hole pressure at high residual gas saturation means that a formation that fosters high residual gas trapping,rather than CO_(2)dissolution in brine,is more likely to experience injectivity issues during the sequestration process.

Application of supervised machine learning to predict the enhanced gas recovery by CO_(2) injection in shale gas reservoirs

The technique of Enhanced Gas Recovery by CO_(2) injection(CO_(2)-EGR)into shale reservoirs has brought increasing attention in the recent decade.CO_(2)-EGR is a complex geophysical process that is controlled by several parameters of shale properties and engineering design.Nevertheless,more challenges arise when simulating and predicting CO_(2)/CH4 displacement within the complex pore systems of shales.Therefore,the petroleum industry is in need of developing a cost-effective tool/approach to evaluate the potential of applying CO_(2) injection to shale reservoirs.In recent years,machine learning applications have gained enormous interest due to their high-speed performance in handling complex data and efficiently solving practical problems.Thus,this work proposes a solution by developing a supervised machine learning(ML)based model to preliminary evaluate CO_(2)-EGR efficiency.Data used for this work was drawn across a wide range of simulation sensitivity studies and experimental investigations.In this work,linear regression and artificial neural networks(ANNs)implementations were considered for predicting the incremental enhanced CH4.Based on the model performance in training and validation sets,our accuracy comparison showed that(ANNs)algorithms gave 15%higher accuracy in predicting the enhanced CH4 compared to the linear regression model.To ensure the model is more generalizable,the size of hidden layers of ANNs was adjusted to improve the generalization ability of ANNs model.Among ANNs models presented,ANNs of 100 hidden layer size gave the best predictive performance with the coefficient of determination(R2)of 0.78 compared to the linear regression model with R2 of 0.68.Our developed MLbased model presents a powerful,reliable and cost-effective tool which can accurately predict the incremental enhanced CH4 by CO_(2) injection in shale gas reservoirs.

CO_(2),N_(2),and CO_(2)/N_(2)mixed gas injection for enhanced shale gas recovery and CO_(2)geological storage

In this work,using fractured shale cores,isothermal adsorption experiments and core flooding tests were conducted to investigate the performance of injecting different gases to enhance shale gas recovery and CO_(2)geological storage efficiency under real reservoir conditions.The adsorption process of shale to different gases was in agreement with the extended-Langmuir model,and the adsorption capacity of CO_(2)was the largest,followed by CH_(4),and that of N_(2)was the smallest of the three pure gases.In addition,when the CO_(2)concentration in the mixed gas exceeded 50%,the adsorption capacity of the mixed gas was greater than that of CH4,and had a strong competitive adsorption effect.For the core flooding tests,pure gas injection showed that the breakthrough time of CO_(2)was longer than that of N_(2),and the CH_(4)recovery factor at the breakthrough time(Rch,)was also higher than that of N_(2).The RcH of CO_(2)gas injection was approximately 44.09%,while the RcH,of N_(2)was only 31.63%.For CO_(2)/N_(2)mixed gas injection,with the increase of CO_(2)concentration,the RcH,increased,and the RcH,for mixed gas CO_(2)/N_(2)=8:2 was close to that of pure CO_(2),about 40.24%.Moreover,the breakthrough time of N_(2)in mixed gas was not much different from that when pure N_(2)was injected,while the breakthrough time of CO_(2)was prolonged,which indicated that with the increase of N_(2)concentration in the mixed gas,the breakthrough time of CO_(2)could be extended.Furthermore,an abnormal surge of N_(2)concentration in the produced gas was observed after N_(2)breakthrough.In regards to CO_(2)storage efficiency(S_(Storage-CO_(2)),as the CO_(2)concentration increased,S storage-co_(2)also increased.The S storage-co_(2),of the pure CO_(2)gas injection was about 35.96%,while for mixed gas CO_(2)/N_(2)=8:2,S sorage-co,was about 32.28%.

Experimental and modeling study of CO_(2)-Improved gas recovery in gas condensate reservoir

This paper presents the effectiveness of the CO_(2) injection process at different periods during gascondensate reservoir development.Taking a real gas-condensate reservoir located in China's east region as an example,first,we conducted experiments of constant composition expansion(CCE),constant volume depletion(CVD),saturation pressure determination,and single flash.Next,a series of water/CO2 flooding experiments were been investigated,including water flooding at present pressure 15 MPa,CO_(2) flooding at 25.53 MPa,15 MPa,which repents initial pressure and present pressure respectively.Finally,the core flooding numerical model was constructed using a generalized equation-of-state model reservoir simulator(GEM)to reveal miscible flooding mechanism and the seepage flow characteristics in the condensate gas reservoir with CO2 injection.A desirable agreement achieved in experimental results and predicted pressure volume temperature(PVT)properties by the modified equation of state(EOS)in the CVD and CCE tests indicated that the proposed recombination method can successfully produce a fluid with the same phase behavior of initial reservoir fluid with an acceptable accuracy.The modeling results confirm the experimental results,and both methods indicate that significant productivity loss can occur in retrograde gas condensate reservoirs when the flowing bottom-hole pressure falls below dew point pressure.Moreover,the results show that CO_(2) treatment can improve gas productivity by a factor of about 1.39 compared with the water flooding mode.These results may help reservoir engineers and specialists to restore the lost productivity of gas condensate.

苏北油田二氧化碳驱油注气工艺应用实践及评价

CO_(2)驱油注气管柱是CO_(2)进入地层的通道,是保证CO_(2)驱油能够成功完成的重要因素之一,苏北油田在充分借鉴调研的基础上,设计、研制了四种CO_(2)驱油注气管柱。对苏北油田使用的4种CO_(2)驱油注气管柱及配套工艺进行了适应性分析,从气密封性、可靠性和经济性等方面进行了对比研究,并对其应用效果进行评价。分析认为,现有的CO_(2)驱油注气工艺可以满足苏北油田大规模注气需求,并取得了一定的增产效果。但在实际矿场试验中发现现有CO_(2)驱油注气工艺还存在一些局限和不足之处,为此提出了对目前CO_(2)驱油注气管柱进行改进完善、扩大应用气密封检测技术、深化CO_(2)驱油注气井油套管脆断机理研究和加强CO_(2)驱油分层注气技术攻关等下步研究建议。