Data collection throughout the exploration stage is of paramount importance, especially for the unconventional projects. Since a vast amount of data is acquired through the well logging, large logging expenditures are usually incurred. In unconventional projects, marginal economics dictate particularly strict budget strategies, including expenditures for logging activities. A significant component of the logging costs is associated with the tool temperature rating. In northern Oman, the bottomhole static temperatures of the tight sandstone gas formation being explored are 175°C [347°F] or higher, which coincides with the upper limit of the conventional logging tools. It has been observed that the tool failure frequency increases dramatically when this limit is approached, leading to repeated logging jobs or regretted (missed) data. The simple way to increase the temperature rating of logging tools to perform at high bottomhole temperatures is to use ceramic electronic boards. However, the cost of this solution is roughly 10 times higher than standard tools. Slightly less costly is acquiring data with logging-while- drilling techniques; this has its own disadvantages, such as logging tool availability and data resolution. Another possible approach is careful assessment of the bottomhole temperature at particular times during logging to enable using conventional tools with lower temperature ratings. The assessment is a challenge itself. Direct measurements are difficult because the temperature gauges on logging tools are affected by heat from the electronic components. It is possible to simulate borehole conditions, but this requires extensive modeling and involves many variables such as cooling from mud circulation; heat transfer among the formation, annulus, and drillpipe; conversion of mechanical energy from drilling to heat; and the addition of hot cuttings to mud. That latter modeling has been performed and verified with the field data in various conditions: vertical and horizontal geometries and different mud types. The study established the achievable bottomhole circulating temperatures at various operations, duration of safe temperature window for less-expensive logging, and the bottomhole temperature profile in various drilling scenarios. This allowed delineating a road map for logging future high-temperature wells in the field.
Saudi Arabia has at today a reported fourth largest reserve of Natural gas in the world and as the fastest growing energy consume in the Middle East it is also consuming the totality of the national gas production, having no net import or exports of Natural Gas. The Natural Gas production and consumption was increased by 62% in the last 10 years and the demand in the country is expected to double the actual capability by 2030. This is the proposed target, and it is expected to be achieved under significant investment of foreign companies that are planning and executing projects related with non-associated gas fields in different areas of Saudi Arabia. Several oil companies are focused in explore, and produce in case of success exploration campaign, from high pressure, high temperature and deep gas reservoirs. The grade of reservoir properties anisotropy including the high uncertainty of pore and fracture pressures in the hostile environment that a conventional drilling practice will face in the deep exploratory wells is not resulting at the end as an efficient and viable way to reach the planned production target. The correct application of a new technology as Managed Pressure Drilling (MPD) has demonstrated the impact in the successful result obtained specifically in Saudi Arabia. This paper is summarizing the planning process behind an MPD project as well as the description of the obtained results in a case history. In the exploratory well project case developed in this paper, the main driver for MPD was to reduce the Non Productive Time usually experienced in other exploratory off-set wells drilled in the same basin by ascertaining in real time the reservoir pressure limits (pore and fracture) controlling mud losses and influx events associated with the new formation drilled. The right determination of the pressure balance between fluid losses and influxes was achieved and the operational window was successfully managed during all the stages of the MPD operation. Traditionally, the high solids content of the drilling fluid used in conventional drilling practices in this area, which main objective is to obtain an extreme overbalanced condition that could overlap the high level of reservoir uncertainties and anisotropy, is also damaging the reservoir itself, impacting the final production and productive life of the well. The content of solids was reduced to the minimum during this MPD operation, managing the annular pressure just by manipulating the MPD equipment adjusting in real time the back pressure exerted from surface. MPD reduced at the minimum the drilling non productive time associated with common hazards usually observed during conventional drilling practices in the same area and also finalized the exploratory well drilled in this deep gas reservoir without report any incident. In addition it has improved the reservoir production compared to the wells that were drilled conventionally.
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