Khalil Shahbazi

The Experimental Investigation of Nitrogen and Carbon Dioxide Water-alternating-gas Injection in a Carbonate Reservoir

Abstract Floods were conducted using rock–fluid systems consisting of carbonate cores from Binak reservoir, which is located in southwest of Iran, oil and brine. The coreflood protocol consisted of a series of steps including brine saturation, absolute permeability determination, flooding with oil to initial oil saturation, endpoint oil permeability determination, and, finally, nitrogen and carbon dioxide water-alternating-gas (WAG) injections. The effect of slug size on oil recovery was investigated using immiscible nitrogen (N2) WAG injection and the amount of oil recovered was compared with continuous injection of N2. Experimental results show that ultimate oil recovery is not very sensitive to changing the slug sizes for N2 WAG injection, although the slug size of 0.15 pore volume (PV) injection is better than others. As less PV is injected, a higher oil production rate is achieved. Also, N2 WAG flood appeared to be better in performance than continuous gas injection (CGI) of nitrogen. Carbon dioxide (CO2) injection was performed in three modes, including CGI, WAG injection, and hybrid WAG. Experimental results show that for optimization of oil recovery in CO2 floods, a continuous gas slug of 0.4–0.5 PV followed by 1:1 WAG needs to be injected.

A New Approach for Predrilling the Unconfined Rock Compressive Strength Prediction

Abstract A reasonable knowledge of rocks physical and mechanical properties could save the cost of drilling and production of a reservoir to a large extent by selection of proper operating parameters. In addition, a master development plan (MDP) for each oilfield may contain many enhanced oil recovery procedures that take advantage of rock mechanical data and principles. Thus, an integrated rock mechanical study can be considered an investment in field development. The unconfined compressive strength (UCS) of rocks is the important rock mechanical parameter and plays a crucial role when drilling an oil or gas well. A drilling operation is an interaction between the rock and the bit and the rock will fail when the resultant stress is greater than the rock strength. UCS is actually the stress level at which rock is broken down when it is under a uniaxial stress. It can be used for bit selection, real-time wellbore stability analysis, estimation an optimized time for pulling up the bit, design of enhanced oil recovery (EOR) procedures, and reservoir subsidence studies. Rock strength can be estimated along a drilled wellbore using different approaches, including laboratory tests, core–log relationships, and penetration model approaches. Although this rock strength profile can be used for future investigation of formations around the wellbore, they are actually dead information. Dead rock strength data may not be useful for designing a well in a blind location (infill drilling). Rock strength should be predicted prior to drilling operations. These sort of data are helpful in proposing a drilling program for a new well. In this research, new equations for estimation of rock strength in Ahwaz oilfield are formulated based on statistical analysis. Then, they are utilized for estimation of the rock strength profile of 36 wells in a Middle Eastern oilfield. An artificial neural network is then utilized for prediction of UCS in any predefined well trajectory. Cross-validation tests showed that the results of the network were compatible with reality. This approach has proven to be useful for estimation of any designed well trajectory prior to drilling.

Inhibition performance and mechanism of Horsetail extract as shale stabilizer

Abstract The Horsetail extract was used as shale stabilizer, its inhibition performance was studied by laboratory experiments and compared with potassium chloride and polyamine, and its anti-swelling mechanism was analyzed. Bentonite inhibition test, sodium bentonite sedimentation test, dynamic linear swelling test, and hot rolling cutting dispersion test were employed. The results show that: the bentonite is not capable of being hydrated or dispersed in solution with the Horsetail extract; the Horsetail extract can reduce the swelling of the bentonite and prevent disintegration and dispersion of cuttings in aqueous medium; the extract is well comparable and competitive with potassium chloride and polyamine in inhibition performance. The constituents of the Horsetail extract have active hydroxyls which are capable of forming hydrogen bounding with surfaces of bentonite particles, leading to decrease of the water absorption on bentonite particles surfaces which results in bentonite swelling reduction. Besides having good anti-swelling ability, Horsetail extract is ecofriendly, readily available and inexpensive.

Prediction of dynamic viscosity of n-alkanes at high pressures using a rigorous approach

Abstract An adaptive neuro-fuzzy interference system has been developed for estimating the dynamic viscosity of n-alkanes in a wide range of operating conditions. In this study, for the first time, a simple predictive model is proposed for viscosity prediction of n-pentane, n-octane, n-nonane, n-decane and dodecane at various pressures and temperatures, especially at high pressures, without needing to measurement or estimation of density. This tool predicts the dynamic viscosity of the n-alkanes as function of pressure, temperature and n-alkanes molecular weight. The obtained results of the model were in an excellent agreement with experimental data with an acceptable coefficient of determination of 0.999 for both training and testing datasets. Moreover, the validity of the proposed model for viscosity trends prediction at various conditions was demonstrated and it showed a very good match with actual data. This model is simple to use and can be of massive evaluation for better understanding the behavior of fluids under reservoir conditions.

Modelling hydraulic fracturing process in one of the Iranian southwest oil reservoirs

ABSTRACT Hydraulic fracturing creates a high conductivity channel within a large area of formation and bypasses any damage that may exist in the near wellbore region. Moreover, it has been one of the major well stimulation techniques to increase well production. In order to model and study the feasibility of implementing this technique in one of the Iranian Southwest oil reservoirs, an extensive literature survey was carried out. One-dimensional mechanical earth model was constructed. Stable mud window was determined and types of failures were diagnosed. Consequently, on these bases, geomechanical feasibility was confirmed and hydraulic fracturing treatment for the case study was designed. Different scenarios were defined and sensitivity analysis was conducted together with the confirmation of economic feasibility. Furthermore, channel fracturing technique was employed and it was found that using this technique can be more suitable and beneficial than conventional fracturing method.

Prediction of Uniaxial Compressive Strength of Underground Formations From Sonic Log Parameters

Selecting the most appropriate bit for any hole section is the key feature in achieving superior drilling performance. This feature has an enormous influence on the optimized performance of drilling and also economically affects the process greatly. The most important factor to correctly select a bit is formation physical characteristics, mainly rock compressive strength. Different sources can be used to obtain rock strength along the wellbore, such as logs, cutting and rock mechanical test, or even drilling data. The use of empirical correlations based on logs is often the only way to estimate strength in many situations due to the absence of cores for laboratory tests. In this study, one of the Iranian oil fields was selected to be analyzed. The goal was calculating the compressive strength from sonic log parameters. In order to develop an exponential correlation, log, drilling data, and backward simulation were used. Log data included sonic, neutron, density, and gamma ray logs. The correlation developed is applicable to determine the quantity of compressive strength of underground formations in absence of cores.

The effect of different solvents on the density of undersaturated athabasca bitumen: Application in VAPEX and ES-SAGD

ABSTRACT Predicting the density of bitumen after solvent injection is highly required in solvent-based recovery techniques like expanding solvent-steam assisted gravity drainage (ES-SAGD) and vapor extraction (VAPEX) in order to estimate the cumulative oil recovery by these processes. Using experimental procedures for this purpose is so expensive and time-consuming; therefore, it is crucial to propose a rapid and accurate model for predicting the effect of various solvents on the dilution of bitumen. In this study, an adaptive neuro-fuzzy interference system is introduced to estimate the effect of methane, ethane, propane, butane, carbon dioxide, and n-hexane on the density of undersaturated Athabasca bitumen in wide ranges of operating conditions. The obtained results were in an excellent agreement with experimental data with coefficients of determination (R2) of 0.99997 and 0.99948 for training and testing datasets, respectively. Statistical analyses illustrate the superiority of the proposed model in predicting the bitumen density at different conditions.

Applying of LSSVM approach as a novel tool for accurate prediction of asphaltene inhibition efficiency

ABSTRACT Asphaltene precipitation is one of critical problems for petroleum industries. There are different methods for inhibition of asphaltene precipitation. One of the common and effective methods for inhibition of asphaltene precipitation is utilizing asphaltene inhibitors. In this work, Least squares support vector machine (LSSVM) algorithm was coupled with simplex optimizer to create a novel and accurate tool for estimation of effect of inhibitors on asphaltene precipitation as function of concentration and structure of inhibitors and crude oil properties. To this end a total number of 75 measured data was extracted from the literature for training and testing of predicting model. The average absolute relative deviation (AARD), the coefficient of determination (R2) and root mean square error (RMSE) of total data for prediction algorithm were determined as 1.1479, 0.99406 and 0.61039. According to these parameters and graphical comparisons the LSSVM algorithm has potential to predict asphaltene precipitation in high degree of accuracy.

Investigating the applicability and effects of hydraulic fracturing technology on well productivity in one of the Iranian gas condensate reservoirs

Hydraulic fracturing is an important method utilized to enhance oil and gas recovery from reservoirs, especially for low-permeability formations. It has been broadly used in gas reservoirs, especially tight formations. Gas condensate reservoirs (GCR) experience a noticeable loss of productivity after achieving dew point pressure and condensate drop out formation around the wellbore, and could be suitable candidates for hydraulic fracturing operations. The aim of this study is to determine the effect of hydraulic fracturing on well productivity of GCR. A single well reservoir model corresponding to the GCR in the South of Iran and another model with similar conditions for hydraulic fracturing were created and validated. Reservoir model simulation was performed using a commercial compositional simulator. Sensitivity analysis was performed on fracture geometry parameters including the fracture length and width, flow parameters such as positive coupling and inertia effect, and reservoir properties namely permeability and fluid condensate gas ratio (CGR). The results demonstrated that hydraulic fracturing in GCR, especially in this case study, noticeably increases the productivity and production plateau time as well as decreases condensate formation, which increasing the fracture length and width intensifies this effect. Moreover, the optimized fracture length was obtained. It was found that the negative inertia effect in low hydraulic fracture widths and positive coupling in high fracture widths are dominant. Hydraulic fracturing is most effective in low-permeability and high-CGR conditions. These results pave the hydraulic fracturing road not only from industrial viewpoint, but also as a guideline for field-scale projects.

The Effect of Weight Material Type on Barite Sag Tendency

Settling of weight materials is a phenomenon that occurs in high-pressure formations where a high mud weight is needed. Barite sag is roughly defined as the change in density due the settling of weight materials that observed when circulating bottoms up following operations such as tripping pipe where the mud has not been circulating for an extended period of time. This may lead to problems such as lost circulation, well control difficulties, poor cement jobs, and stuck pipe in oil industry. In deviated wells, the settling distance to the lower side of the wall is small in comparison to vertical wells. This leads to rapid generation of solids beds and consequently, sag problems are particularly severe in deviated wells. The authors present the settling rate of different weight materials in muds with mathematical method. Furthermore, it investigates the effect of weight material type and hindered settling factor on settling rate. Moreover, the type of weight materials for barite sag management is recommended.