Aqueous phase trapping (APT) as a kind of mechanical formation damage can occur in porous medium when water based well bore fluids come into contact with a formation which exhibits sub-irreducible initial water saturation. Such type of formation damage commonly occurs during drilling using water based fluids in tight gas reservoirs and in depleted conditions in rich gas retrograde condensate reservoirs and is a major mechanism of damage in these reservoirs. Evaluating reservoir's potential for APT is of great importance where the reservoir is susceptible to APT, since well productivity can be improved through proper evaluating and consequent attempts to reduce associated formation damage. This can be done using APT laboratory tests on reservoir rock samples. But, due to some restrictions, an alternative approach is followed which is use of predictive formulas. During the last fifteen years, number of formulas has been proposed to evaluate the reservoir's potential for APT. In this paper a full procedure for evaluating and minimizing formation damage through APT is described. Different formulas used for evaluating the sensitivity of a suspect reservoir to APT are reviewed. A new formula for evaluation of gas reservoir's potential for APT is presented; CAPT or coefficient of APT. Using information of some gas reservoirs, the comparison is made between predictions made by different formulas. Comparisons show that CAPT predicts true gas reservoir's potential for APT and is more accurate than other formulas.

In some Iranian oil fields hydrocarbon recovery is mainly from sandstone reservoirs and sand production is a major problem in these fields. Main reason of sand production in these reservoirs is due to unconsolidated sandstone layers. The common method to decrease this problem is achieved by installing mechanical sand control systems. Previously, some techniques of sand control have been used in Iranian oil fields, such as gravel packing, slotted liner and chemical consolidation by resin. The results which have been obtained through these methods are not remarkably good enough in some cases. Expandable sand screen (ESS) is a new technique in sand control that can result in lower skin and consequently improves reservoir inflow performance. Field tests in various conditions have shown very satisfactory results in both open and cased hole applications. This paper will provide a brief overview of ESS and its advantages and will explains some of the concerns deal with ESS well completion. It provides details of well production results before and after installation of ESS. It also suggests that the use of ESS as an alternative to conventional sand control methods in Iran oil fields is preferable specially in cased hole completed wells.

Multilateral drilling (ML) drilling technology is one of the unconventional drilling methods to increase the productivity of a well. It is thought that ML wells could be more economic with higher productivities than other types of wells such as vertical, directional, horizontal or extended reach horizontal wells. Advances in ML drilling has resulted in significant cost saving, greater flexibility and increased profit potential. In the last two decades, thousands of ML wells have been drilled worldwide. Around 10 percent of the total wells are ML. During 1980s, advances in horizontal technology were adopted quickly in the Middle East to bring about dramatic improvements in well productivity. Many operators in the Persian Gulf region looked at ML drilling technology as a next step from horizontal drilling technology. These operators started to drill ML wells after experiencing successful drilling of horizontal wells. Since the early 1990, the use of ML drilling technology in the Middle East has seen significant growth to the extent that Middle East is one of the most active areas in the world for ML applications. This paper investigates the benefits of ML drilling as one of the highly expanded methods. Advantages and challenges of the ML technology are highlighted. Since Middle East is one of the most active areas in the world for ML applications, therefore, two case studies from this region are reviewed. The first case study is the first Saudi Aramco's deep ML gas well, and the second is drilling a dual lateral well in Dukhan field in Qatar. For the former case study, productivity of ML wells is presented. Furthermore, a comparison is made between the productivity of a horizontal and dual ML in order to give a recommendation for one of them. Introduction Unconventional drilling is a growing part of the global drilling activity. In the past several years directional, horizontal, extended reach horizontal and multilateral (ML) wells have been drilled successfully using unconventional drilling techniques. Unconventional drilling technologies play a key role today where conventional technologies are not fully efficient to keep development profitable. These technologies allow us to increase production per well but also to improve ultimate reservoir recovery factor (RF). ML drilling as one of unconventional drilling techniques emerged at the beginning of nineties.1 The general definition of a ML well is one in which there is more than one horizontal or near horizontal lateral well drilled from a single side (mother bore) and connected back to a single bore. 2 During 1980s, advances in horizontal technology were adopted quickly in the Middle East to bring about dramatic improvements in well productivity. Many operators in the Persian Gulf region looked at ML drilling technology as a next step from horizontal drilling technology. These operators started to drill ML wells after experiencing successful drilling of horizontal wells. Since 1992, the use of ML drilling technology in the Middle East has seen significant growth to the extent that Middle East is one of the most active areas in the world for ML applications. 3 In 1996, it is estimated that over 35 MLs were drilled in the Middle East. 4 Among the Middle East countries, some invested more on of ML technology are Saudi Arabia, UAE, Oman, and Qatar. Examples of leading companies in the region in ML technology are Saudi Aramco and ZADCO. Other countries in the region are progressing in application of ML technology. An overview to applicability of ML technology in the Middle East countries has been done by Mirzaei Paiaman and Moghadasi (2009).5

In Drilling Oil Wells a system of complex fluids and chemical additives is used. Losses of these fluids in the well during drilling or disposal of them in well site could transfer pollutants to groundwater. In the present study a number of well sites, located in South of Iran, were studied to indicate types and magnitude of various pollutant materials that remain in the environment undestroyed and have considerable impacts on the underground water resources. Hydrocarbons used in Oil Base Muds (OBM) that can't be biodegrade readily in nature found to be the most severe pollutant material caused by disposal of Drilling Mud and Cuttings. Volume of drilling waste for these oil wells evaluated to be an average almost 0.5 m3 per one meter of drilled oil well. Available common treatment methods were compared to assess the most economically and environmentally attractive treatment scenarios. Thermal desorption and reserve pit without treatment are two most dominant methods could be conducted in Southern Oil Fields of Iran, each has its advantages and disadvantages. Due to geological structure and near surface aquifer in Khuzestan province thermal desorption should be conducted to disposal cuttings to reduce their hydrocarbon content to less than 5% according to European Standard. Major challenges of drilling waste management program in onshore oil fields of Iran were studied and clear principals for managing waste streams, which include: reduce, replace, reuse, recycle, recover, treat and final dispose, were listed along with material, equipment and strategies that should be considered in each step. Introduction Oil well drilling operations are responsible for the disposal of large quantities of drill cuttings and fluids. On a site of oil drilling, mud provide several important functions, lubrication of drilling bits, the maintenance of subsurface pressures, and transport of cuttings towards surface. It is a complex system of fluids based on water (WBM) or on oil (OBM), with several chemical and mineral additives. The formulation of these muds is adjusted with precision according to the physicochemical conditions of drilling, which change with the depth, and the nature of the crossed geological formations [3]. Other than the fluid (either water or oil or both) and the solid phases, different types of chemicals and polymers are used in designing a drilling mud to meet some functional requirements such as appropriate mud rheology, density, mud activity, fluid loss control property etc. Though the factors that guide the choice of a fluid base and the mud additives are complex, the selection of the additives must take account of both the technical and environmental factors to eliminate any environmental impact [4]. Due to potential detrimental effect of non-environment friendly drilling fluids, Environmental Protection Agency (EPA) and other regulatory bodies are imposing increasingly stringent regulations on the use and disposal of non-environment friendly drilling fluids, whether it is water-based or oil-based [4].

First horizontal well in Iran was drilled in July 1992 in Marun oil field. Since then, most of the Persian giant oil fields have experienced horizontal drilling. This can be considered as a step towards improved recovery. In this paper we try to compare the productivity of vertical and horizontal wells in a particular field. This field is located in the Southern part of Iran, with two separate carbonate reservoirs, R1 and R2. R1 is on the top and R2 in the bottom. An impermeable layer separates the two reservoirs. In this field about 50% of drilled wells are horizontal. Production results from horizontal wells are not satisfactory, and in most cases productivity index of horizontal wells is equal or even less than vertical wells, therefore the reasons should be investigated.