The paper presents the recent development of marginal oil and gas accumulations in the vicinity of the offshore Hidra field, by Total Austral operator and partners Deminex and Pan American Energy. Lying 12 km off the Coast of Tierra del Fuego in 35 m of water, the Hidra field was originally developed in 1989-1990 with conventional deviated wells drilled from two wellhead platforms, Hidra Centro and Hidra Norte. In 1996, three ER wells were drilled with a jack-up from these platforms to tap the Ara Sur and Hidra Sur accumulations. Although technical difficulties had to be overcome, the project was successfully completed. The first well (HNP-7) reached a horizontal departure of 6.2 km at 1700 m TVD representing more than twice the reach of previous conventional wells. This experience established the feasibility and cost effectiveness of ER wells, as a means of developing marginal oil deposits. Total and its partners decided to launch a second, more ambitious campaign in 1997, in which 9 ER wells were planned to be drilled, this time from the coastline. By May 1998, after a year of operations, 5 wells had been completed including the new American Continent record ER well, AS-3. Drilled late 1997 to a maximum departure of 7973m at a vertical depth of 1615 m, giving a HD/TVD ratio of 4.9, AS-3 was drilled and completed in 90 days. This technical achievement was the reward of intense engineering preparation, proactive attitude on the part of the project team and multidisciplinary teamwork and efficient risk management. The engineering preparatory studies are described, together with the rig mobilization, modifications and drilling operations highlights. A primary consideration of this project is protection of the unspoiled environment at the drilling site. The utter remoteness of the location has added a significant degree of difficulty to an already challenging task. An effort has been made with the mud logging company to improve the monitoring of hole condition, especially during the critical 12 1/4" phase, which reached 6700 m in length, at 80-85 inclination, using a device which measures in real time the total amount of cuttings flowing at the shale shakers. This data is combined with Pressure While Drilling data to further estimate hole cleaning efficiency and ECD. To overcome friction, the 9 5/8" casing of well AS-3 was run to 7720 m MD in flotation, requiring careful engineering and unconventional procedures and equipment. Landing into and drilling through the Springhill reservoir which is only 10 to 20 m thick and can exist locally in lenses, requires delicate geosteering techniques. This paper lists the main challenges that had to be overcome and the techniques employed. An economic comparison with other more conventional development schemes is outlined. The results achieved so far open the way to more ambitious targets which are presently under evaluation. P. 99
fax 01-972-952-9435. AbstractThis paper presents an innovative solution to monitor hole cleaning in Extended Reach Wells. It was successfully used while developing marginal oil and gas reserves offshore TIERRA DEL FUEGO (ARGENTINA) by TOTAL AUSTRAL operator and partners DEMINEX and PAN AMERICAN ENERGY.Keeping the hole clean in Extended Reach Wells is a key issue as cuttings accumulation will result in increased torque, pressure losses and will create a high risk of getting a stuck pipe.Cuttings Flow Meters (CFM) continually measure and record the flow of cuttings at the outlet of the shale shakers. This measurement allows an enhanced understanding of hole cleaning process and status, which in turn permits to optimize the main drilling parameters such as flow rate, rotation, circulation times, reaming time at connections and rate of penetration.It has been observed on those wells that the volume of cutting returns always fits with the actual volume of hole, over extended periods of time. By comparing on a permanent basis the volume of hole drilled with the volume of cuttings returned to surfiace, one can monitor the cuttings accumulation in the hole, one can thus better diagnose an increase in hole friction, adjust mud rheology parameters and circulating rate in order to minimize the surface and bottom hole circulating pressures while ensuring a good transport, all factors which are essentiat to further extend the drilling envelope.
The growing interest in deeply buried reservoirs increasingly leads operators into extreme drilling conditions characterized by high hydrostatic pressure (over 20.000 psi) and high temperatures (over 300 °F), combined with hard formations (high CCS-40,000+ psi). Drilling in such environments requires specific adaptations of well design and in equipment selection. Additionally, these wells present multiple issues in well control, drilling and completion operations, and make the entire operation technically more complex and financially more risky.Referencing the specific example of drilling operations, the great depths and increased formation compaction leads to very low rates of penetration (ROP) and considerably extended operation time. These low ROPs equate to low depth of cut, and as a direct consequence the typical size of the drilled cuttings recovered at the shakers is extremely low (0.020 to 0.20 mm). This makes the cuttings irrelevant for the purpose of geological identification of the formations. This situation occurs with both impregnated diamond and PDC drill bits in these applications at low ROPs. If the downhole conditions (HPHT) exceed the MWD or LWD specifications, accessing critical geological information will necessarily require a challenging coring job, dramatically increasing the operation time and thus the cost of the well.
The drilling of hard formations usually requires specific drilling systems to achieve an efficient rate of penetration. Due to the limited depth of cut, the solution often involves the use of high RPM drive systems such as turbines or high speed motors and a fixed cutter product is usually the drill bit of choice. With increasing well depth the roller cone option is normally avoided due to the low penetration rates and limited rotating hours obtainable with these drill bits. Roller cone use invariably leads to multiple trips and a significant increase in the time and cost of the drilling operation, especially for deeply buried reservoirs where hard rocks are generally encountered and bit diameter is reduced at TD. Unavoidably, in some applications roller cone bits continue to be used in order to obtain the quality cuttings necessary for the geologist to correctly assess the formation. This is typically the case when the reservoir interval is encountered and exact formation knowledge is critical. A new drilling solution has been developed to address this situation and is presented in this paper. The idea consists of a fixed cutter bit which leaves the center of the hole uncut. The lack of bit center leads to the creation of a core. This core is broken by the bit itself and ejected at the side through a specifically designed junk slot. The core is then carried to the surface along with the other cuttings. This process leads to very high quality cuttings for surface examination. The improvement is especially important where normal cuttings quality is poor due to the use of turbines or high speed motors together with impregnated diamond bits. Importantly, as the center part of the bit is uncut this new technology also provides a significant increase in the rate of penetration. In a fixed cutter bit the center is one of the most inefficient cutting areas as the rotational speed of the cutter is low to null. By removing the center, an increased ROP efficiency in the range of 15 to 25 percent can be obtained depending upon the bit diameter. The field tests that are presented in the paper show quantifiable improvements in terms of geological sample quality, cutting efficiency and drilling cost reduction.
Deeply buried reservoirs are one of the main options to extend the oil & gas reserves and to keep on satisfying the growing need of energy. In this context, the ability to determine the temperature profile of the mud while drilling is a crucial issue from the design of a well to the control of the rheological properties of the mud. The present work is a study of the heat transfers occurring between the mud and the formation while circulating in a well. Firstly, a model, based on an empirical Nusselt law, was built and implemented in a numerical software. Secondly, we compared the results found with the numerical software with field data, which was made possible thanks to the collaboration of Total. Introduction The estimation of the "peak oil" relies on the knowledge of the identified and recoverable oil & gas reserves. Currently, the producing countries still estimate their reserve to contain enough oil & gas for another 40 years of production. Several ways exist to keep this estimation and postpone the "peak oil", among which is the production of deeply buried reservoirs. This is a challenge the producing oil companies will have to take up. Nevertheless, the deeper the drilling, the bigger the pressure and thermal constraints are. High pressure and high temperature mandate the development of new technologies such as drilling fluid which is able to keep its rheological properties. The mud has to maintain its efficiency in:–removing the cuttings from the well–stabilizing the borehole to prevent any collapse of the well–cooling down, cleaning and lubricating the bit–controlling the fluid loss–suspending the cuttings in case of a pump stoppage In this context, it is important to be able to assess the temperature of the drilling mud and to make predictive calculations of the mud temperature while drilling. This information would be priceless for the mud engineer, mud logger, drilling engineer, etc., to help to choose the right composition of mud at the right time (E. Gao et al. 1998 and B. Corre et al. 1984), especially when the temperature reaches the threshold when MWD tools do not work anymore. That's the reason why we worked on building a model which correctly represents the heat exchange phenomena between the mud and its environment. Ultimately, the goal is to be able to accurately predict the temperature profile of the mud all along the well with potential applications in real time monitoring or well design. State of the Art Showing the level of interest in the topic, there have been a number of papers which have been written about the mud temperature when circulating in a well.
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