Decline curve based models for predicting natural gas well performance

The productivity of a gas well declines over its production life as cannot cover economic policies.To overcome such problems,the production performance of gas wells should be predicted by applying reliable methods to analyse the decline trend.Therefore,reliable models are developed in this study on the basis of powerful artificial intelligence techniques viz.the artificial neural network(ANN)modelling strategy,least square support vector machine(LSSVM)approach,adaptive neurofuzzy inference system(ANFIS),and decision tree(DT)method for the prediction of cumulative gas production as well as initial decline rate multiplied by time as a function of the Arps'decline curve exponent and ratio of initial gas flow rate over total gas flow rate.It was concluded that the results obtained based on the models developed in current study are in satisfactory agreement with the actual gas well production data.Furthermore,the results of comparative study performed demonstrates that the LSSVM strategy is superior to the other models investigated for the prediction of both cumulative gas production,and initial decline rate multiplied by time.

Improving the radiopacity of Fe-Mn biodegradable metals by magnetron-sputtered W-Fe-Mn-C coatings:Application for thinner stents

In this exploratory work,micrometric radiopaque W-Fe-Mn-C coatings were produced by magnetron sputtering plasma deposition,for the first time,with the aim to make very thin Fe-Mn stents trackable by fluoroscopy.The power of Fe-13Mn-1.2C target was kept constant at 400 W while that of W target varied from 100 to 400 W producing three different coatings referred to as P100,P200,P400.The effect of the increased W power on coatings thickness,roughness,structure,corrosion behavior and radiopacity was investigated.The coatings showed a power-dependent thickness and W concentration,different roughness values while a similar and uniform columnar structure.An amorphous phase was detected for both P100 and P200 coatings while γ-Fe,bcc-W and W_(3)C phases found for P400.Moreover,P200 and P400 showed a significantly higher corrosion rate(CR)compared to P100.The presence of W,W_(3)C as well as the Fe amount variation determined two different micro-galvanic corrosion mechanisms significantly changing the CR of coatings,0.26±0.02,59.68±1.21 and 59.06±1.16μm/year for P100,P200 and P400,respectively.Sample P200 with its most uniform morphology,lowest roughness(RMS=3.9±0.4 nm)and good radiopacity(~6%)appeared the most suitable radiopaque biodegradable coating investigated in this study.

Numerical approach for enhanced oil recovery with surfactant flooding

The remained oil in the reservoir after conventional water-flooding processes,forms a dispersed phase in the form of oil drops which is trapped by capillary forces and is almost about 70%of the original oil in the place(OOIP).To reduce oil residual saturation in laboratory experiments and field projects,surfactant flooding is effective via decreasing the interfacial tension mobility ratio between oil and water phases.Estimation of the role of design variables,like chemical concentrations,partition coefficient and injection rate in different performance quantities,considering a heterogeneous and multiphase oil reservoir is a critical stage for optimal design.Increasing demand for oil production from water-flooded reservoirs has caused an increasing interest in surfactant-polymer(SP)and alkali-surfactant-polymer(ASP).Modeling minimizes the risk of high cost of chemicals by improving our insight of process.In the present paper,a surfactant compositional flood model for a three-component(water,petroleum and surfactant),two phase(aqueous and oleic)system is studied.A homogeneous,two-dimensional,isothermal reservoir with no free gas or alkali is assumed.The governing equations are in three categories:the continuity equations for the transport of each component,Darcy's equation for the transport of each phase and other auxiliary equations.The equations are solved by finite-differences using a procedure implicit in pressure and explicit in saturation.The validation of the model is achieved through comparing the modeling results with CMG simulators and BuckleyeLeverett theory.The results of modeling showed good agreement with CMG results,and the comparison with BuckleyeLeverett theory is explained according to different assumptions.After validation of the model,in order to investigate sensitivity analysis,the effects of system variables(partition coefficient,surface tension,oil viscosity and surface injection concentration)and performance variable(cumulative oil recovery)are studied.Finally,the comparison of oil recovery between water-flooding and surfactant-flooding was done.The results showed higher oil recovery with changes in capillary number when the partition coefficient is greater than unity.Increasing oil viscosity resulted in decreasing the oil recovery by changing in fractional flow.Moreover,it was concluded that the oil recovery was enhanced by increasing surfactant injection concentration.The oil recovery was increased when surfactant was injected to the system and this result was obtained by comparing water-flooding and surfactantflooding.

On the evaluation of steam assisted gravity drainage in naturally fractured oil reservoirs

Steam Assisted Gravity Drainage(SAGD)as a successful enhanced oil recovery(EOR)process has been applied to extract heavy and extra heavy oils.Huge amount of global heavy oil resources exists in carbonate reservoirs which are mostly naturally fractured reservoirs.Unlike clastic reservoirs,few studies were carried out to determine the performance of SAGD in carbonate reservoirs.Even though SAGD is a highly promising technique,several uncertainties and unanswered questions still exist and they should be clarified for expansion of SAGD methods to world wide applications especially in naturally fractured reservoirs.In this communication,the effects of some operational and reservoir parameters on SAGD processes were investigated in a naturally fractured reservoir with oil wet rock using CMG-STARS thermal simulator.The purpose of this study was to investigate the role of fracture properties including fracture orientation,fracture spacing and fracture permeability on the SAGD performance in naturally fractured reservoirs.Moreover,one operational parameter was also studied;one new well configuration,staggered well pair was evaluated.Results indicated that fracture orientation influences steam expansion and oil production from the horizontal well pairs.It was also found that horizontal fractures have unfavorable effects on oil production,while vertical fractures increase the production rate for the horizontal well.Moreover,an increase in fracture spacing results in more oil production,because in higher fracture spacing model,steam will have more time to diffuse into matrices and heat up the entire reservoir.Furthermore,an increase in fracture permeability results in process enhancement and ultimate recovery improvement.Besides,diagonal change in the location of injection wells(staggered model)increases the recovery efficiency in long-term production plan.

Prediction of sand production onset in petroleum reservoirs using a reliable classification approach

Controlling sand production in the petroleum industry has been a long-standing problem for more than 70 years.To provide technical support for sand control strategy,it is necessary to predict the conditions at which sanding occurs.To this end,for the first time,least square support machine(LSSVM)classification approach,as a novel technique,is applied to identify the conditions under which sand production occurs.The model presented in this communication takes into account different parameters that may play a role in sanding.The performance of proposed LSSVM model is examined using field data reported in open literature.It is shown that the developed model can accurately predict the sand production in a real field.The results of this study indicates that implementation of LSSVM modeling can effectively help completion designers to make an on time sand control plan with least deterioration of production.