With the increased global demands on oil and gas, operators strive to maximize production by conducting more advanced drilling operations, such as extended reach, horizontal and high-pressure/high-temperature (HP-HT) drilling and are expanding globally into drilling unconventional resources. Unconventional gas resources offer significant gas production growth potential in the coming years, currently accounting for 43% of the US gas production. Tight Gas Sands (TGS) represents approximately 70% of the unconventional production and significant reserves are yet to be developed. Although "tight gas sands" are an important type of basin-centered gas reservoir characterized by low permeability, abnormal pressure, gas saturated reservoirs and no down dip water leg., not all of the TGS are Basin-centered gas (BCGAs). An intensive technology effort to both better understand tight gas resource characteristics and develop solid engineering approaches is necessary for significant production increases from this low-permeability, widely dispersed resource. Gas production from a tight-gas well will be low on a per-well basis compared with gas production from conventional reservoirs. A lot of wells have to be drilled to get most of the oil or gas out of the ground in unconventional reservoirs However, economical production of TGS is very challenging as it exists in reservoirs with micro-Darcy range permeability and low porosity but has a huge potential for production in the future. Poor permeability results in lower gas production rates from TGS reservoirs. In order to economically develop TGS resources an advanced technology has to be developed and implemented. Most of the TGS reservoirs are characterized by being thick (hundreds to thousands of feet thick) and multilayered where their gas production rates can be enhanced by hydraulic fracturing. Although service companies have large capabilities for conventional/unconventional reservoirs but the used technology to drill, complete and stimulate tight gas reservoir is quite complex and the results are often unexpected and unforeseen. The appropriate completion methods and stimulation techniques in these reservoirs are dependent on many parameters and variables, such as depth, pressure, temperature, capillary and overburden pressures and the number of sand layers. This paper provides a technical overview of the state of the art technology used to develop those reservoirs. This work takes a multidisciplinary approach to better understand how gas can be produced from tight gas sand reservoirs. Two real case histories will be presented and discussed; Travis Peak formation in eastern Texas, USA; and Risha gas field in eastern Jordan.

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAlmost every drilling operation is a potential source of damage to well productivity, lost circulation, differential sticking and other related conventional Drilling problems.This paper re-visits the key damage mechanisims and provides a broad overview on how they occur during various oilfield operations, and their effect on well productivity. Also, lost circulation or fluid invasion potential in high permeability zones, large open fractures, heterogeneous carbonates with massive interconnected vugular porosity, or pressure depleted zones would be a major issue of concern during conventional drilling condition. The worst-case scenario would be a combination of one of these high permeability features with significant pressure depletion.In order to overcome the above problems while drilling, the industry developed a method to drill with a bottom hole pressure below the pore pressure, called Underbalanced Drilling -UBD As the majority of hydrocarbons being exploited today are found in existing pressure depleted or complex and lower quality Reservoirs with lots of the conventional drilling problems, this is where Underbalanced Drilling Technology can add value and in some cases reduce development cost. Soon, Underbalanced Drilling will become the standard field development technique, both Onshore and offshore, where the Geology and Reservoir are suitable.The paper reviews several case histories and real results highlighting the advantages of Underbalanced Drilling Technology in reducing Formation Damage, Lost Circulations and improving well productivity.

The increased demand for more sources of clean energy such as natural gas from unconventional reservoirs has forced the industry to explore the more challenging tight gas reservoirs. Tight gas reservoirs constitute a significant proportion of the world's natural gas resource and offer great potential for future reserve growth and production. However, to meet future global energy demand, access to tight gas reservoirs requires innovative and cost effective technical solutions.Yet, tight gas reservoirs are often characterized by complex geological and petrophysical systems as well as heterogeneities at all scales. Exploring and developing tight gas accumulations are both technically and commercially challenging due to the large subsurface uncertainty and low expected ultimate recovery per well. In addition, formation damage is an undesirable operational and economic dilemma that may occur during any phase of gas recovery from tight gas reservoirs. Tight gas reservoirs normally show significant damage during well drilling, completion, stimulation and production. Therefore, they may not flow gas at optimum rates without advanced production improvement techniques.The main damage mechanisms and the factors that have significant influence on well productivity in tight gas reservoirs include mechanical damage to formation rock, plugging of natural fractures by mud solid particles invasion, relative permeability reduction around wellbore as a result of filtrate invasion, liquid leak-off into the formation during fracturing operations, water blocking, damage due to wellbore breakouts, compression damage and the damage associated with perforation. Drilling and fracturing fluids invasion mostly occur through natural fractures and may also lead to serious permeability reduction in the rock matrix that surrounds the natural or hydraulic fractures.Prevention, control and remediation of formation damage are among the most important issues to be resolved for efficient exploitation of tight gas reservoirs. Designing certain chemicals and/or treatment procedures for damage control and remediation is not an easy scientific and engineering task. Good understanding of the formation damage mechanisms would allow operators to make informed decision as to the best practices to drill, complete and produce tight gas wells.In this paper, a review of commonly practiced methods and tools available for prevention, control and remediation of formation damage will be discussed and presented.

The proposed well is an exploratory well where the formation pressures were estimated based on the experience in drilling offset wells in the area. The 8 3/8" and 5 7/8" hole sections, have a wide range of predicted pore pressure, indicating a considerable span of uncertainty in addition to other related conventional drilling problems as tight hole and gas influx. In previous wells drilled in the area, many drilling problems and wellbore stability issues were experienced. One of the possible cuases of the mechanical instability could be attributed to the large fluctuations in the bottom hole pressure that is intrinsic to conventional drilling practices. These fluctuations are originated from the stopping and starting of drilling fluid circulation during jointed pipe connections, specifically, they result from the fluctuation in the equivalent circulating density (ECD), which occurs when the pumps are turned on and off. This fluctuation could triger a kick-Loss scenario that increases the Non Productive Time (NPT). drilling-related flat time further indicate a necessity for a technology that enables more precise wellbore pressure management.Constant Bottom Hole Pressure (CBHP) which is variation of MPD, is applicable to avoid changes in ECD by applying appropriate levels of surface backpressure, a technique that maintains constant bottom-hole pressure during the complete drilling operation. The primary objective of drilling this well using the Managed Pressured Drilling technology was to reach the target depth with minimum drilling complication, avoid uncontrolled event by maintaining a constant bottom hole pressure and properly managing the well in case an underbalanced condition occurs while drilling the 8 3/8" and 5 7/8" hole sections.As with any advanced drilling technique, successful application of MPD technology required a detailed understanding of the potential benefits as well as limitations. This paper summarizes the process that was used to identify, plan, and implement MPD as a technology to drill the well to the target depth and prevent conventional. Planning and operational results are presented in this paper.