Underbalanced drilling is in fact the best drilling method for oil reservoirs that their pressure has been reduced. This study aimed at obtaining a criterion for estimating the minimum and maximum underbalanced presUnderbalanced drilling is an advanced technology and a drilling operation in which the drilling fluid pressure inside the well is less than the pore pressure of sures of the drilling mud for enhancing oil recovery and preventing damages to the formations in the Iranian carbonate reservoirs. To this end, data on 13 wells in various Iranian oil fields were first collected. The oil wells were simulated at different drilling mud pressures with the help of the finite difference method (FDM)-FLAC2D. The elastoplastic normalized yielded zone area (NYZA) method was used for stability analysis and estimation of the minimum and maximum underbalanced pressures of the drilling mud. The NYZA diagram was plotted separately for each well. Considering the drilling mud pressures on the NYZA diagram in the range of NYZA=1 to the pore pressure, a minimum and maximum drilling mud pressure of NYZA=1 and NYZA=0.2 was calculated, respectively. Eventually, a correlation was proposed as a fraction of the pore pressure to estimate the minimum and maximum underbalanced pressures. This correlation is expressed as a factor or fraction of the pore pressure. The minimum and maximum underbalanced pressures of the drilling mud to enhance oil recovery and prevent damage to the formation can be estimated solely by inserting the pore pressure of the formation in this correlation.

Due to the growing demand in the oil industry, the application of enhanced oil recovery (EOR) techniques for oil reservoirs to meet the needs of communities is essential. nowadays, nanotechnology is growing rapidly and it contribute significantly to the technological advances in many industries and in various oil and gas fields such as exploration, drilling, enhanced oil recovery and refining and distribution. In this paper, the effect of nanoparticles, nanoemulsions, nanofilters, nanogels, nanosensors, nanorobots, and nanocatalysts in enhanced oil recovery and oil reservoirs progress and new achievements in this field are discussed. The results show that, nanotechnology has the potential to change the common methods of EOR by improving geomechanics of the reservoir and surface tension alongside modification of oil reservoirs. Today, this subject has attracted the attention of many researchers.

Wettability is an important parameter that influences the petrophysical properties of reservoir rocks. When drilling is doing، the penetration of mud filtration into formation causes considerable wettability alteration and affects the oil displacement by water. Hence the enhanced oil recovery methods will be affected because of formation damage. In this study، the effect of three samples (a bentonite commonly used in oil well drilling، a purified bentonite، and nanoclay) on wettability of sandstone and carbonate rocks has been studied using the contact angle method. The modification of surface properties of montmorillonite sheets by hydrophobic plug reformer changed the wettability of the clay particles from water-wet to oil-wet. This change resulted in the suitable dispersion of nanoclay (organic) into oil phase (as hydrophobic phase). The contact angle measurements of the prepared suspension from each of three samples showed that common and purified bentonites altered the wettability of the sandstone and limestone rocks to water wet، whereas the nanoclay changed contact angle to oil-wet behavior. Based on these observations، use of nanoclay، as an oil-based drilling mud additive، is useful due to its compatibility with oil zone wettability and suitable dispersion in oil-based drilling fluid.

Drilling unit is the main asset of upstream oil and gas industry which is utilized for the drilling or well work over in exploration, development and enhanced oil recovery operations. The issues concerning Offshore Drilling Units have more complexities due to their locations which are at sea and the requirements governing them; hence, from legal point of view, the status of the mentioned Units is controversial issue which is ambiguous not only in international law but also in Iran law. The legal status of Offshore Drilling Units may impact on the jurisdiction that states exercise over them. This issue emphasizes the importance of analysis of their legal status. Therefore, this article aims to analyze the different developed theories whether Offshore Drilling Units can be regarded as ship or artificial island or whether they have dual status or specific and separate status (category) and then it determine the best legal status of Offshore Drilling Units that can be responsive to the needs of oil and gas industry.

Rapid increasing demand for energy necessitates the development of oil and gas fields in a more accurate and reliable method which includes the optimization of drilling and production operations in conjunction with enhanced oil recovery methods. The technique of directional drilling plays a significant role in this regard and affects the drilling performance and producing wells. Prevention of the destruction and damages on the walls of the well is an important task including the selection of the optimal pressure of drilling mud to be injected.In this study we investigated and modeled one of the directional wells in the Southern Iranian oil field-Cheshmeh Khosh; which includes the determination of the role and effect of drilling mud pressure on the extent of formation damage. The results of the study show that optimal injection pressure of 60 Mpa give better out comes specifically reduces the displacement of points on the walls.

In the oil and gas industry, different kinds of nanoparticles have been studied and reported to enhance various oil and gas operations. In this review however, the focus is on identifying different applications of aluminum oxide (Al2O3) nanoparticles in the petroleum industry because of its various potentials. Al2O3 nanoparticle has been reported to be a good enhanced oil recovery agent that can alter rock wettability, reduce oil viscosity and reduce interfacial tension between oil and water. Al2O3 nanoparticle militates against kaolinite mobilization during hydrocarbon production, improves rheological properties in drilling fluids, improves the quality of cementation during well installations, and improves engine performance and thermal efficiency in brakes. Al2O3 nanoparticle has the capacity to inhibit growth of microbes, it is a catalyst in crude oil refining, it eliminates asphaltene from crude oil and is used to detect water oil interface. In biodiesel, Al2O3 nanoparticle reduces emissions and enhances fuel consumption.

The continuous development of global economy with decreasing in available hydrocarbon sources and increasing discovery and extraction costs due to decrease in-situ oil and gas reservoir, displays the necessity of using new techniques for the improve rate of penetration and productivity in well. Nanotechnology has already contributed significantly to technological advances in the energy industries. Nanotechnology has the potential to introduce revolutionary change in drilling industry. Nanotechnology produces nanomaterials with many attractive properties, which can play an important role in intensifying mud cake quality, reducing friction, eliminating differential pipe sticking, maintaining borehole stability, protecting reservoir, and enhancing oil and gas recovery. Nano fluids can be designed by adding nano-sized particles in low volumetric fractions to a fluid. The nano particles modify the fluid properties, and suspensions of nano-sized particles can provide numerous advantages. This paper presents an extensive literature review of assessing the applications of nanomaterials in drilling and drilling fluids, and evaluates the potential technical benefits that these nanomaterials might provide to petroleum development and production.

considering the status of Oil and Gas Industry, for Increasing oil production capacity, there are only two ways ahead; Firstly, further exploration and discovery of new oilfields and secondly increasing and improving the oil recovery of reservoirs which is known in the industry literature as "Enhanced Oil Recovery" and "Improved Oil Recovery". Increasing the recovery rate by a few percent can have a significant impact on the daily output volume and ultimately on the country's oil revenues. This article seeks to analyze and represent the position of this concept in the legal and contractual system of the country, especially the new model of Iranian Oil Contracts (IPC), to offer suggestions for establishing a suitable contractual framework for such projects. Analysis of the legal system of Iran and the contractual models used (such as Buy-back contracts) indicate that these contracts do not meet the requirements and risks of these fields. It seems that the suggestions presented in this article could act as general conditions governing contracts in this field and serve the interests of the country in these contracts.

In this study, using the results of performed shale formation Characterizatins and the history of drilling in Iranian oil fields, an environmentally friendly water based drilling fluid is designed to replace the oil based drilling fluids. This drilling fluid has desirable properties in drilling water sensitive formations. New drilling fluid additives including shale inhibitors, new polymers and sized solid particles have been used to prepare this new drilling fluid. The most important properties of this new drilling fluid are controlling the mud filtrate and pressure invasion to the formation, clay mineral alteration and activity reduction, improvement of the integrity of drilling cuttings, reduction in formation damage, stability at high temperatures, stability in acidity changes and the compatibility by drilling fluids dilution during drilling operation. The lubricity and shale cuttings recovery of this new drilling fluid are better than those of other similar water based drilling fluids. Replacing this drilling fluid by oil based drilling fluids in drilling industry will be a great means to protect the environment and drilling personnel in addition to being economically advantageous.