查看更多>>摘要：The wellhead is an important component in the context of well integrity and operational safety,as it serves as a link between well and riser in offshore oil wells.Wellheads,combined with the BOP and/or the Christinas tree,act as the final barrier element preventing leakage of oil from the well into the environment.The wellhead must sustain loads from the casings(soil reaction),which are hung into it through the casing hangers,as well as sustain loads from the riser(waves,current),which is connected at the top of the BOP(right above the wellhead)through the lower flex joint.In Part I of this work,we propose a deterministic methodology to evaluate wellhead motions,considering a mechanical system that couples the vessel,the riser,the wellhead itself,the conductor and surface casings,and their interaction with the soil.The limiting factor in this study is the excessive motions experienced by the wellhead,which can lead to well integrity problems such as dislodgment of the conductor casing or a poor cementing job.The simulation of this system provides the motions experienced by the wellhead,through simulation of some well design choices(use of jetting base,conductor casing size,and cemented conductor).Results have shown that modern 5-phase wells with cemented conductor confer higher integrity to the wellhead compared to old 4-phase wells with jetted conductors,while the jetting base has not affected the wellhead motions significantly.These results are extended in Part II,which incorporates a stochastic analysis.
查看更多>>摘要：Practice has proved that drag reduction oscillators can be used to decrease the axial friction and increase wellbore extension effectively in sliding drilling.However,the complicated mechanical behaviors of drillstring with drag reduction oscillators have not been revealed sufficiently,and there has no theoretical method to optimize drag reduction parameters.In this paper,an optimization design model of drag reduction oscillators is built with drag reduction efficiency as the target,and the mechanical model of drillstring with drag reduction oscillators is established by considering the friction nonlinearity.Further introducing the initial conditions,boundary conditions,and continuity conditions,the finite differential equation of drillstring vibration is obtained and solved.Next,combined with the oscillation propagation length and the installation position optimization models,the orthogonal experimental design method is applied to optimize the relevant parameters.In the optimization process,the constraint factors,including drillstring failure and hydraulic loss,are considered.Finally,the new model is applied to a field case study,in which the drag reduction effects of drillstring with and without oscillators are compared,and the impact of relevant factors on drag reduction are analyzed.The results show that the equivalent friction coefficient near the oscillator installation position is significantly reduced,whereas the hook load and weight on bit(WOB)are increased significantly with drag reduction oscillators.With the increase of amplitude or frequency,the propagation distance of the oscillator increases.The amplitude of vibration force and the number of oscillators are the two main factors affecting drag reduction efficiency.Three hydraulic oscillators with vibration amplitudes of 40 KN are recommended,and the drag reduction efficiency is 51.78%.However,excessively large oscillation amplitude may lead to drillstring failure and too many oscillators will increase the hydraulic loss a lot.Therefore,there are optimal values of oscillation amplitude and the number of oscillators.The research results are of significant guiding significance for optimal design and safety control of drag reduction oscillators in sliding drilling.
查看更多>>摘要：Fracturing(hydraulic fracturing technology)treatment in an unconventional reservoir was a key technology.For an increased in production,effective proppant placement in hydraulic fracture systems was important in operating conditions.Especially,two key factors,proppant transportation distance and packing height,determined the final conductivity and gas production.This study aimed to develop a new type of proppant and evaluated its properties.Based on two new types of materials that could modify the surface of the proppant and fiber,the fiber and proppant coupled with each other due to the surface treatment and could transport longer and pile up higher in the fracture.Therefore,to furtherly figure out this new proppant property,visual fracture models were designed and used with some key factors.This study showed that this new proppant had some remarkable properties and had a better transportation efficiency in visual fracture models.The findings of the study were as follows:(1)The fully coupled fiber-proppant(FCFP)had high grafting distributed channel rate and pavement efficiency in both fresh water and slick water.(2)The FCFP formed a cellular pattern in the fracture and established high-porosity channels.The findings might guide the new operation technology,optimize operation parameters,improve proppant transportation efficiency,and maintain a good proppant distribution in fracture systems in the future.
查看更多>>摘要：Use of robust products is of utmost importance in the subsea production systems to ensure the maximum utilization of the energy resources available under the seabed.To achieve highly reliable products,a comprehensive technology qualification program is proposed in this paper for the subsea electrical and electronics-based products.The recommended qualification program is specifically focused on a novel technology readiness level 4(TRL4)process of the product used in an intended environment condition,which guarantees the product availability on the seabed without any operational failures.The analytical assessment on the products'design,operating conditions and compliance stress tests are proposed following the internationally recognized standards,e.g.The American Petroleum Institute(API),International Electrotechnical Commission(IEC),Institute of Electrical and Electronics Engineers(IEEE),International Organization for Standardization(ISO),European Standards(EN)and European Union(EU-directives).Modified environmental tests methods and novel product safety procedures are introduced for the first time to ensure that products meet the acceptance criteria set in the proposed TRL4 process.Finally,the proposed TRL4 process and its recommended test methods are exercised on the various functional units of the subsea electronic module.The experimental results show that the product is fit for use in the subsea environment after going through the proposed extensive qualification test program.
查看更多>>摘要：Tight oil and gas reservoirs with huge development potential are widely distributed all over the world and horizontal well technique is a popular development technology for such kinds of reservoirs.However,the efficiency of conventional horizontal well technology is usually unsatisfying due to the unfavorable flow conditions caused by the nature of tight reservoirs,such as low matrix permeability and narrow pore throat.Multi-stage fractured horizontal well technology is an emerging attractive technology that can greatly improve oil production by generating highly conductive fracture networks in tight reservoirs,and numerical simulation method is generally used to predict the production dynamics of the multi-stage fractured horizontal wells.Nevertheless,the complex geological conditions of reservoirs would greatly increase the difficulties and time required to implement a complete simulation(including model building and calculation).Therefore,in this paper,deep convolution generative adversarial networks(DCGAN)based on U-Net framework was applied to establish the dynamic mapping relationship between fracture pattern and reservoir pressure during the production process,that is,the dynamic reservoir pressure distribution can be obtained by image mapping the fracture distribution details.The results showed that the efficiency of U-Net framework based deep convolution in extracting,dividing and splicing the geometric features of fracture network is significant,and the generative adversarial networks model can effectively predict the reservoir pressure distribution according to the fracture network geometry after being trained with 6000 sets of data.Herein,the training accuracy of the proxy model towards sample data was compared,and the confrontation between the generator and the discriminator in the iterative training process was clarified according to the error function.Furthermore,the prediction accuracy towards pressure distribution at different fracture network geometry scales by the proxy model was compared.Results indicated that the pressure diffusion range predicted by the proxy model is basically consistent with the range obtained from the numerical simulation,with a mean square error(MSE)generally smaller than 0.2.In addition,the relationship between the prediction accuracy of the proxy model and the number of sample data and iterative training times was also studied,which showed that the mean square error of the proxy model kept decreasing with the increasing iteration cycles and sample size,which met the basic law of statistical learning.Moreover,it is worth mentioning that the proposed method may also shed light on the applications of DCGAN in other reservoir-related problems.
查看更多>>摘要：The hydration and swelling caused by the contact of shale with water during oil and gas drilling have caused many difficulties in drilling operations.Water-based drilling fluids(WBDFs)are considered to be more environmentally friendly and economical than oil-based drilling fluids(OBDFs).However,shale inhibitors are needed to solve the problems of shale hydration swelling caused by water.Reducing water content and liquid intrusion are effective ways to prevent the interaction between water and shale.Extensive researches have been conducted to develop highly effective shale inhibitors that inhibit shale swelling and reduce drilling costs and environmental impact.Especially in recent years,environmentally friendly shale inhibitors with low toxicity have become the main research object.A good shale inhibitor should not only have the ability to efficiently reduce shale hydration swelling,but also need to be compatible with other components of the drilling fluid to develop an effective high-performance WBDF.Besides,the requirements of environmental regulations should be met.Only biodegradable environmentally friendly inhibitors can develop the green and sustainable oil and gas industry.Some researchers have published some reviews about shale inhibitors,but there has been no review about low toxic and environmentally friendly shale inhibitors considered as the trend of the oil and gas industry.The purpose of this paper is to provide a detailed review of inhibitors with low toxicity and environmentally-friendly in recent years,aiming to fully understand the current methods of shale hydration inhibition and provide new ideas for the subsequent research on shale inhibitors.
查看更多>>摘要：Water flooding is one of the common techniques for increasing petroleum reservoirs'pressure and production life.Seawater(SW)is a preferable choice for waterflooding because of its high availability and low cost.However,SW could be incompatible with formation water(FW)and causes to precipitate inorganic minerals and reduce reservoirs'permeability.A method for preventing inorganic scales is using scale inhibitors(SIs)which need more precise studies to find the critical factors for achieving better efficiency.In this study,the effect of Hydroxyethylenediphosphonic Acid(HEDP)and 2-Phosphonobutane-1,2,4-Tricarboxylic Acid(PBTC)on preventing inorganic scales formation were studied in three stages.In the modeling step,mixing FW and SW was simulated by PHREEQC software.In the second step,as static experiments,the inhibitor efficiency(IE)of two SIs were compared.At dynamic experiments,the performance of Sis in carbonate rocks was studied by core flooding tests.ICP analyses were taken on solutions for interpreting results measured in both static and dynamic scenarios.Results indicated that the ionic composition of SW and FW plays a vital role in types of inorganic scales deposition.PHREEQC software could predict type and amount of scales although its prediction is 9% more than experimental results.It was shown that although Sis could mitigate precipitating inorganic minerals,they have different performances in each concentration.While HEDP is more effective in lower concentrations,PBTC's efficiency will improve with rising its concentration.Elemental analysis showed 100 ppm HEDP has %65 IE which is the most efficient SI.The results of dynamic experiments demonstrated that HEDP and PBTC have a pleasing inhibitory effect in carbonate rocks.The presence of Sis in SW could decrease formation damage during flooding into carbonate reservoirs.
查看更多>>摘要：At present,the stimulation technique involving soaking after fracturing of shale gas reservoirs has received increasing attention.In this study,gas-water displacement experiments were carried out to simulate the contact state between the fracturing fluid and the shale during the soaking stage after hydraulic fracturing of the shale gas reservoir.By using low-field nuclear magnetic resonance to dynamically monitor the occurrence state of the methane in shale cores,the changes in the masses of the methane in different occurrence states were calculated.Furthermore,the displacement of the adsorbed methane in the shale by the fracturing fluid was studied.In addition,the influences of the fracturing fluid's salinity and the shale clay content and type on the displacement process were also analyzed.The results of this study show that the fracturing fluid has a stronger adsorption on clay minerals than that of methane,so it can replace the adsorbed methane in the shale.Compared with pure fracturing fluid solution,the high salinity fracturing fluid solution containing cations has a stronger adsorption on the clay minerals in the shale,and thus,it has a stronger displacement ability.The mineral composition of the shale reservoir also has an important influence on the displacement efficiency.The higher the content of clay minerals with high adsorption capacities,the more adsorbed methane is replaced.The results of this study are important for gaining a better understanding of the stimulation technique involving soaking after fracturing of shale gas reservoirs and for optimizing the design of soaking.
查看更多>>摘要：The content of ductile grains and grain packing texture have great influence on the quality of sandstone,especially tight sandstone.A new simulation method for ductile grain deformation during compaction in sandstone under triaxial stress servo based on the discrete element method(DEM)was established.The micro-mechanical parameters for the simulation were obtained using physical experimental data in the literature.The numerical simulation results of single ductile grains and sandstone with ductile grains confirmed the reliability of the simulation method,where the effect of grain crushing,cementation and dissolution on porosity evolution were not considered.The simulation and physical experiment results show the porosity of sandstone decreases linearly with the increase of ductile grain content.The relationship between porosity and effective stress can be predicted using exponential model,when the grain packing texture was one-component nature packing texture dominated and ductile grain content was less than 50%.When the grain packing texture changes to binary packing and the content of ductile grains was less than 50%,the porosity evolution curve show some fluctuations,and the monitoring compaction curve showed that the relationship between effective stress and porosity can not be represented by exponential model.The void ratio changes of sandstone with binary packing texture during compaction can be predicted based on grain packing texture,and the correlation coefficient between the predicted and simulated void ratio changes(Ae)were high,the average errors accounts less than 6% of the average of void ratio changes(Ae)when the content of ductile grains were less than 25%.The errors between predicted and simulated void ratio changes(Ae)based on packing texture increases with the increase of ductile grain content.When the content of ductile grains exceeded 50%,the exponential model was no longer applicable for sandstone,while the logarithmic model is better.In addition,the proposed simulation method is significant for the study of porosity evolution process and the quantitative evaluation of the relative importance of its diagenesis in sandstone having ductile grains.
查看更多>>摘要：Several laboratory studies observed wettability alteration of carbonate rocks towards a more water-wet state through modifying the composition of injected water.The change in carbonate surface charge was reported as the underlying reason behind this wettability alteration and the corresponding incremental oil recovery by engineered water injection(EWI).Although the reported results of carbonate rock sensitivity to injected water ionic strength,pH,salinity,and concentration of potential determining ions(Ca~(2+),Mg~(2+),and S0_4~(2-)),there is still an ambiguity on the way carbonates interact with injected water/ions.This is due to the different miner-alogical compositions and electrokinetic properties of carbonates.Therefore,this paper provides more insight into the role of major rock-forming carbonate minerals(calcite and dolomite)in engineered water injection at different water compositions by utilizing surface complexation modeling(SCM).The study utilizes a geochemical simulator to highlight the effect of dolomite surface complexation reactions.After determining the total rock surface charge and surface potential,the disjoining pressure was calculated to estimate the water film thickness and consequently,infer about wettability alteration.The results showed that a successful EWI operation creates three regimes:displacement regime,surface reaction regime,and quasi-equilibrium regime.These regimes can be characterized by the proposed surface complexation technique to calculate/optimize the injection pore volumes needed for each regime,determine the location of EWI effect in the reservoir,and predict the time ranges when EWI will reach to the surface in the form of additional oil recovery.Also,it was found that the surface reaction regime is the most important one where main surface reactions and oil recovery occur.Furthermore,the study utilizes SCM for both calcite and dolomite minerals for the first time highlighting their importance in geochemical reactions of EWI when the rock has dolomite in its composition.Existing SCM considers oil-brine and rock-brine interfaces where only calcite mineral is captured in the rock-brine interface.The latter is based on assuming that the rock composition is pure calcite,which is not necessary the case.The findings of this study confirm that seawater is capable of inducing wettability alteration in carbonates under certain favorable conditions due to adsorption/desorption of the potentially determining ions.
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