Iranian Journal of Oil and Gas Science and Technology

Abstract Fishing operations are one of the most essential parts of drilling operations. If the fishing operation fails, the other direction should be considered to continue drilling and reach the desired depth, which can be achieved using sidetracking operations. Long-term fishing operations increase the cost and time of the drilling operation; therefore, we should try to have a successful fishing operation in the shortest possible time. It can be stated that the execution of the fishing operation is economical as long as the costs are less or at least equal to the cost of the sidetracking operation. Therefore, the optimal fishing time must be determined to make the drilling operation economical. Many statistical analysis methods have been used to determine the optimal time, but they are not popular due to insufficient accuracy and time-consuming calculations. This study used a machine-learning (ML) model with a regression algorithm to estimate the optimal time for fishing operations in the Gachsaran oil field. The fishing cost rate and depth as input data were first collected and categorized based on different sections of the Gachsaran oil field to calculate the optimal fishing time. Then, the sidetracking cost was predicted by the machine learning model, and this cost was equated to the fishing cost in the worst conditions. As a result, the optimal fishing time was calculated for each section. The result showed that the model could estimate the cost of sidetracking with an error of less than 2%. Using the designed model and the input data of the Gachsaran oil field, considering the optimal fishing time, it was possible to save $1 million and 16 h in drilling a well.

Abstract Oil recovery from oil-wet carbonate rock is a significant challenge in the oil industry. The present study investigates the influence of the natural surfactant Hawthorn leaves extract (HLE) on oil recovery from carbonate rock. Two chemical surfactants, sodium dodecyl sulfate (SDS) and dodecyl tri methyl ammonium bromide (DTAB), were used to validate and compare oil recovery with the new natural surfactant HLE. A wettability alteration test using the contact angle method, an interfacial test (IFT) using pendant drop, and core flooding were employed to investigate the behavior of the surfactants on oil recovery. The experimental results show that the critical micellar concentration (CMC) point of different concentrations of HLE, SDS, and DTAB solution occurs at 3.25, 3.00, and 4.06 wt %, respectively. In wettability alteration, the natural surfactant HLE is more effective than other chemical surfactants (SDS and DTAB) at the CMC point. As observed, the contact angle of the carbonate pellet and the HLE at the CMC point is 86°, and this angle for SDS and DTAB is 112° and 92°, respectively. The core flooding results show that the oil recovery factor improves from 37% with water flooding to 47.6% with SDS, 56.2% with DTAB, and 54.7% with HLE. The results prove that this new natural surfactant (HLE) can be used as a novel surfactant for the chemically enhanced oil recovery process in carbonate oil reservoirs. HLE has beneficial effects in oil recovery because of its environment friendly compared to SDS and DTAB.

Abstract In recent years, the use of natural surfactants as surface active agents in chemical methods of oil recovery over chemical surfactants has been under consideration due to the absence of environmental problems. In this study, a new plant, Albizia julibressin (Albizia), was introduced as a natural surfactant. Our novelty resides in a unified approach that deals with the introduction of Albizia julibressin (Albizia) as a new natural surfactant, interpretation of the chemical EOR objectives, interface reactions, and the induced optimization to improve oil recovery. For this purpose, the plant was extracted using Soxhlet extraction method, aqueous base solutions and interfacial tension between natural surfactant aqueous solutions and kerosene as an oil phase were measured by pendant drop method. The critical micelle concentration structures formed by this material has been determined by interfacial tension tests and confirmed by electrical conductivity tests. The results show that Albizia extract at 3.5 wt% begins to form micelles structures, which is the critical concentration of Albizia plant micelles. At this concentration, the interfacial tension between the deionized water and the oil phase is reduced from 34 mN /m to 10 mN/m, which indicates a significant decrease in interfacial tension by this plant. Carbonate rock was employed to core flooding experiments in order to investigate the effect of Albizia extract (AE) on oil recovery. Also based on results, by using AE, wettability of oil-wet carbonate rocks, was altered from about 165.02◦ to 86.59◦. Finally, AE enhanced ultimate oil recovery about 11.6% of original oil in place in tertiary recovery for a carbonate rock.

Abstract Water flooding is one of the most influential methods for pressure maintenance and enhanced oil recovery. However, water flooding is likely to develop the formation of oilfield scale. Scale formation in reservoirs, due to the mixing of injection water and formation water, could cause formation damage and production limit. Therefore, it is necessary to simulate the compatibility of brine and injection water. Scale prediction is performed using many thermodynamic and/or kinetic based models. In this study, simulations with speciation (ion pairing) are studied, which is a thermodynamic based tool. The utilization of reservoir conditions, formation water analysis, and sea water analysis as the inputs in this method resulted to the accurate prediction of potential scales. In this study, the factors impacting on the scale potential such as pH, temperature, and mixing ratio were also investigated. The obtained results showed that calcite and aragonite were the major scale potential to precipitate. Finally, the results illustrated the important effect of pH and temperature on different scales formation.

Abstract Hydrochloric acidizing is a routine operation in oil fields to reduce the mechanical skin. In this paper, practical acidizing in a typical carbonate oil reservoir located in the southwest of Iran is practiced, which shows an unexpected improvement after acidizing. To understand the acidizing effect on reservoir rock, the formation rock is analyzed on different scales. An acidizing laboratory test is also carried out on formation core samples to understand the acidizing performance. The results show that the main feature of this reservoir is its dominated secondary porosity and its special pattern of distribution. Practically, this porosity percolation has caused high mechanical skin during drilling and a large productivity improvement after acidizing. The acidizing increased the ultimate recovery of the reservoir with existing wells and prolonged the production plateau.

Abstract The unwanted addition of salt to drilling causes flocculation which has an adverse effect on mud rheological properties. To treat the flocculated mud chemical, deflocculants are commonly used; however, their disadvantages such as negative environmental effects, lower tolerance to contamination, and toxicity motivated scientists to search for effective additives. Using plant derived additives instead of commercial additives could help resolve the mentioned weaknesses, because they are nontoxic, cheap, easily accessible, and act multi-functional. In this paper the effect of black myrobalan rheological properties of flocculated bentonite mud was investigated and its performance was compared with chrome lignosulfonate (CLS). Rheological and filtration tests were conducted and properties such as plastic viscosity, yield point, gel strength, thixotropy, and apparent viscosity were calculated. It was perceived that by increasing black myrobalan concentration to 0.6 wt.%, rheological parameters and filtration loss decreased by 50% and 66.3% respectively, but they increased at higher concentrations, which indicated that black myrobalan acted as a deflocculant up to 0.6 wt.%. The deflocculation behavior of black myrobalan at low concentrations is attributed to ellagitannic acid and tannic acid. The comparison of the enactment of black myrobalan with chrome lignosulfonate showed that black myrobalan had a stronger decreasing effect on the rheological parameters and filtration compared to CLS.

Abstract Fluid invasion from water-based drilling mud (WBDM) into the shale formations causes swelling, high pressure zone near the wellbore wall, and eventually wellbore instability problems during drilling operations. For the stability of the wellbore, physical plugging of nanoscale pore throats could be considered as a logical approach toward avoiding the fluid invasion into the shale formation. This paper reports the effect of silica nanoparticles (NPs) as a physical sealing agent on the water invasion into Kazhdumi shale. To this end, pressure penetration apparatus was implemented. Typical WBDM in contact with Kazhdumi shale at different concentrations of NPs with different sizes was studied. The results indicated that the addition of NPs to the WBDM decreased water invasion into Kazhdumi shale. WBDM having 10 wt.% of 25 nm NPs reduced fluid invasion up to 72.76%.

Abstract Reservoir characterization plays an important role in different parts of an industrial project. The results from a reservoir characterization study give insight into rock and fluid properties which can optimize the choice of drilling locations and reduce risk and uncertainty. Delineating hydrocarbon bearing zones within a reservoir is the main objective of any seismic reservoir characterization study. In the current study, using limited well control and seismic data, an attempt was made to predict the productive zones of a reservoir using elastic impedance inversion. Elastic impedance logs at near and far angles of incidence have been crossplotted to find the desired productive parts of the formation. Two partial angle stack seismic data have been inverted using a model-based post-stack seismic inversion. The crossplot of the two inverted volumes is interpreted based on the results from the well location. Finally, the hydrocarbon bearing zones of the reservoir was delineated according to the seismic crossplot analysis.