Analysis of Spatial Distribution Pattern of Reservoir Petrophysical Properties for Horizontal Well Performance Evaluation-A Case Study of Reservoir X

Introduction: Building a large number of static models to analyze reservoir performance is vital in reservoir development planning. For the purpose of maximizing oil recovery, reservoir behavior must be modelled properly to predict its performance. This requires the study of the variation of the reservoir petrophysical properties as a function of spatial location. Methods: In recent times, the method used to analyze reservoir behavior is the use of reservoir simulation. Hence, this study seeks to analyze the spatial distribution pattern of reservoir petrophysical properties such as porosity, permeability, thickness, saturation and ascertain its effect on cumulative oil production. Geostatistical techniques were used to distribute the petrophysical properties in building a 2D static model of the reservoir and construction of dynamic model to analyze reservoir performance. Vertical to horizontal permeability anisotropy ratio affects horizontal wells drilled in the 2D static reservoir. The performance of the horizontal wells appeared to be increasing steadily as kv/kh increases. At kv/kh value of 0.55, a higher cumulative oil production was observed compared to a kv/kh ratio of 0.4, 0.2, and 0.1. In addition, horizontal well length significantly affects cumulative oil production of the petroleum reservoir studied. Results: At kv/kh of 0.55, the results of the analysis showed a rapid decrement in cumulative oil production as the horizontal well length decreases. Considering horizontal well length of 3000 ft, 2000 ft, and 1500 ft, a minimum cumulative oil production was obtained from a horizontal well length of 1500 ft. Conclusion: The geostatistical and reservoir simulation methods employed in this study will serve as an insight in analyzing horizontal well performance.

Study of Influences of Fracture Additives on Stability of Crude Oil Emulsion

Background: A hydraulic fracture is a key technology to increase production of the low permeability oil fields. Fracture additives such as gels, friction reducers, pH adjusters and clay stabilizers were injected into the underground. While more than 50% of the fracture fluid remains underground. The residue of fracture fluid comes out with the produced liquid (a mixture of crude oil and water) in the subsequent oil recovery process, which results in a highly stable crude oil-water emulsion. Objective: The stability and stable mechanism of the emulsion with fracture fluid have been experimentally investigated. Materials and Methods: The influences of fracture additives and components of crude oil on the stability of emulsion were investigated by bottle test and microscopic examination. The interfacial tension and modulus of dilation were explored by a spinning drop interfacial tension meter and an interface expansion rheometer, respectively. Results: The fracture additives played the key role on the emulsion stability. On one hand, the interface energy of oil-water was reduced by friction reducer (IFT was decreased from 24.0 mN/m to 1.9 mN/m), which was a favor for the formation of an emulsion. On the other hand, the dilational modulus of crude oil-water film was increased by hydroxypropyl guar and pH adjuster (Na2CO3) to form a viscoelastic film, which resulted in a highly stable emulsion. Conclusion: The residual fracture fluid accompanied by produced liquid resulted in a highly stable emulsion. The emulsion with fracture additives was difficult to be broken, which may affect the normal production of the oil field. A positive strategy such as developing demulsifier with high efficient should be put onto the schedule.

Experimental Study of the Contamination Effects of Gachsaran Formation Fluid on the Heavy-weight Drilling Fluid

Introduction:Gachsaran Formation is the cap rock of Asmari oil reservoir located in southwestern of Iran. The formation consists of halite, anhydrite, and tachyhydrite, The most important feature of this formation is the presence of high-pressure fluid.Method:Drilling companies have to use heavy-weighted mud to drill the high-pressure formation. Sometimes the weight of drilling fluid is used, up to 2.65(gr/cm3). Although heavy-weight mud prevents formation fluid to flow into the well, it is difficult to maintain and control its properties. If the hydrostatic pressure is insufficient, the formation connate fluid penetrates into the drilling mud and contaminates it.Result:The study found that the symptoms of this contamination lead to an increase in calcium, magnesium, carbonates, and bicarbonates levels, as well as a decrease in pH. The drilling fluid rheology also affected by the contamination.Discussion:Then, method of curing this event is discussed. Prevention, the best treatment for this event was introduced. It was also found that, as soon as contamination signs appear, immediately increase the drilling fluid weight as much as possible, and then adjust the pH between 10.5 and 11.5. The maintain method described is continued until section drilling ends.

Evaluating the Effects of Monovalent and Divalent Salts on the Rheological Properties of Water Based Mud

Introduction:Drilling fluid selection plays a key role in preventing major problems encountered during drilling operations such as hole pack-off, stuck pipe and loss circulation. Mud contamination which results from the overtreatment of the mud system with additives or foreign material entering the mud system during drilling operations causes unwanted changes in the properties of the mud. This makes the mud system inefficient in performing its major roles. This research studies the effects of monovalent and divalent salts namely Potassium Chloride, Calcium Chloride, and Magnesium Chloride on the rheological properties of water-based mud system which is most vulnerable to contamination.Methods:Sixteen mud samples were formulated of which fifteen were contaminated each with different concentrations (0.75 g, 1.50 g, 2.50 g, 3.50 g, and 5.0 g) of the various salts at ambient temperature.Results:The results showed that the rheological properties such as plastic viscosity, apparent viscosity and yield point of the mud samples decreased as the concentrations of various salts increase.Conclusion:It was concluded that increase in the concentration of the salts resulted in a decrease in the rheological properties of the mud samples. This indicates that with the monovalent and divalent salt contamination, there is a significant decline in the performance of drilling mud since the salts affect the dispersion, hydration and flocculation behaviour of the particles. The effect was more profound with CaCl2 and MgCl2 salts than the KCl salt.

Evaluation of the Percolation Sensitivity of Loose Sandstone Using Digital Core Technology

Background:The integrity of the extracted core in loose sandstone gas reservoirs is poor, and because hydration and collapse easily occur, it is difficult to evaluate the sensitivity characteristics accurately by the traditional core flooding experiments.Objectives:We instead investigate the stress sensitivity and water sensitivity of the formation water soaking time using digital core technology.Methods:We take the core of a loose sandstone gas reservoir as a research object and begin by scanning the core samples with a CT scanner. A three-dimensional image of the core can be obtained, the digital information extracted, the pore structure of the porous media mapped directly to the network, and a digital core established using the principles of fractal geometry. The three-dimensional pore network model can also be extracted. Next, we can compare and correct the results calculated by the model based on the real core experimental results, and an objective and effective digital core model can be obtained.Results and Conclusion:Finally, we can calculate the different effective stress, pore throat parameters (pore throat radius, shape factor, coordination number, pore-throat ratio) and relative permeability of different formation water injury times. The research results demonstrate that in sandstone gas reservoir development, as the effective stress continuously increases, the rock pore-throat parameters continue to decrease, and the permeability of the reservoir rock ultimately declines by more than 43.2%. Clay minerals will expand after the edge and bottom water intrude into the reservoir and soak it for a long time: the pore throat is significantly narrowed within 30 days, while after 30 days more, the pore throat undergoes any only slight further changes, and the final permeability decline of the reservoir rock is up to 5.7%. The research results provide important basic petrophysical data for the development of loose sandstone gas reservoirs which, in turn, provide a scientific basis for formulating a reasonable gas production rate in a gas reservoir.

Modelling of Sub-Sea Gas Transmission Pipeline to Predict Insulation Failure

Background: Thermally insulated subsea production and transmission systems are becoming more common in deep-water/ offshore operations. Premature failures of the insulation materials for these gas transmission pipelines have had significant operational impacts. The ability to timely detect these failures within these systems has been a very difficult task for the oil and gas industries. Thus, periodic survey of the subsea transmission systems is the present practice. In addition, a new technology called optic-fibre Distributed Temperature Sensing system (DTS) is now being used to monitor subsea transmission pipeline temperatures; but this technology is rather very expensive. Objective: However, this study proposed a model which will not only predict premature insulation failure in these transmission pipelines; but will also predict the section of the transmission line where the failure had occurred. Methods: From this study, we deduced that in gas pipeline flow, exit temperature for the system increases exponentially with the distance of insulation failure and approaches the normal operation if the failure occurs towards the exit of the gas pipe. This model can also be used to check the readings of an optic-fibre distributed temperature sensors. Result and Conclusion: After developing this model using classical visual basic and excel package, the model was validated by cross plotting the normal temperature profiles of the model and field data; and R-factor of 0.967 was obtained. Analysis of the results obtained from the model showed that insulation failure in subsea gas transmission pipeline can be predicted on a real-time basis by mere reading of the arrival temperature of a gas transmission line.

Lattice Boltzmann Simulation of Natural Convection in a Fractured Petroleum Reservoir Domain: Single-Phase and Multi-Phases Investigations

Background:Natural convection is one of the main effective production mechanisms in a fractured petroleum reservoir.Objective:This paper investigated the simulation of natural convection heat transfer in a fracture domain of petroleum reservoir.Methods:This is done by using Lattice-Boltzmann Equation (LBE) method. In this study, a D2Q9 lattice model was coupled with the passive-scalar lattice thermal model to represent density, velocity and internal energy distribution function, respectively.Results and Conclusion:The results were in excellent agreement with CFD results from the literature. The effects of Rayleigh number and Aspect-Ratio (AR) on flow pattern and temperature distribution were studied. The results indicated that natural convection rate increased with the Rayleigh number increment. The local Nusselt number (Nu) was evaluated on the hot wall and it was rising with increasing the Rayleigh number. Streamlines and temperature field were affected significantly by changing the aspect-ratio. Moreover, first of all, natural convection in Single Component Mutli-Phase (SCMP) was discussed and here and then after validation of SCMP model, the results indicated that the streamline and isotherm were affected by second phases because of the formation of two-phase flow in some of the reservoirs or production period.

Analyzing Effects of Multi-Wall Carbon Nanotubes (MWCNT) & Polyethylene Glycol (PEG) on Performance of Water Base Mud (WBM) in Shale Formation

Background: Due to importance and unique properties of Multi-Wall Carbon Nanotube(s) (MWCNT), in the present study, effectiveness of these materials in Water Base Mud (WBM) is evaluated. Objective: The impacts of mud additives, local water and the addition of phases of bentonite and surfactants on the rheological properties, water loss and stability of water base mud in the absence of Multi-Wall Carbon Nanotube have been experimentally investigated. Materials and Methods: Then, the same experiment performed in the presence of Multi-Wall Carbon Nanotube to determine the efficiency and impact of Nanoparticles (NPs) on the properties of water base mud. The results have shown that additives, local water, Multi-Wall Carbon Nanotube dimensions, addition phase of bentonite and surfactants have influenced the rheological properties of the water base mud. Results: When Multi-Wall Carbon Nanotubes and polyethylene glycol alone or together are added, the performance terms of rheological properties decrease as by the subsequent order CNT; CNT + PEG; PEG. Multi-Wall Carbon Nanotube improves shale integrity and increases shale recovery. Conclusion: In general, the presence of Multi-Wall Carbon Nanotube increases the efficiency of polymers and rheological properties of the water base mud and eventually the shale stability is achieved.

Wiper Trips Effect on Wellbore Instability Using Net Rising Velocity Methods

Background:This paper discusses the wiper trip effects on well instability in shale formations.Objectives:Problematic shale interval sections have been studied for the time spent on the wiper trip operations. Lifting efficiency and well wall instability change with the time analyzed. Detailed drilling operation, formation heterogeneity, rheological and filtration characteristics of polymer water-based mud are discussed. Physical and chemical properties of the drilled formation and drilling fluid are also studied.Materials and Methods:Wiper trips are analyzed using a typical drawing program to find the relations between the most controllable parameters. For that, two calculation models have been implemented to find the net rising cutting particles velocity in the annular. The relation between the net rising velocity and wiper trips is analyzed. Laboratory works have been done to support the findings of field work.Results:Strong relations have been found between the wiper trip impacts and lithology types of the penetrated shale.Conclusion:A modified drilling program is proposed in relation to changes in casing setting depth and drilling fluid properties that make the operations more efficient in cost and time.