Feasibility Study for a Horizontal Well in a High-Pressure and Temperature Environment

Santarelli, F.J.; Dardeau, Claude; Zurdo, Christian

doi:10.2118/25051-ms

Cited by 3 publications

(1 citation statement)

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“…The drilling of wells under ever more difficult conditions such has greater depth, longer phase duration, high pressure and high temperature environment [1], etc, has revealed a crucial need for better understanding of borehole stability under various loading conditions. The main thrust of recent research in this area has used the continuous medium concept (continuum mechanics), as it was believed that the average length between natural fractures in rocks was always large enough when compared to common wellbore diameters [2,3].…”

Section: Introductionmentioning

confidence: 99%

Drilling Through Highly Fractured Formations: A Problem, a Model, and a Cure

1992

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It is usually accepted that wellbore instabilities are caused by either or both an excessive stress concentration at the borehole wall and the chemical reactivity of the formation. Assuming good hole cleaning, common cures for such instabilities are therefore mud density increase and/or change of the mud system. However, even though these methods have proved highly successfull when drilling through intact formations, the same may not stand when it comes to highly fractured rocks. The purpose of this paper is to describe the studies performed in order to allow the safe drilling of a particularly troublesome, highly fractured formation which had led previously to several successive side tracks.The efficiency of the different attempts at solving the problem are analysed in the light of the various side tracks. The core taken during one of these side tracks was analysed, showed that the formation was highly fractured and chemically inert, and provided many parameters for the modelling of the problem which was performed by a discrete element programme. Further modelling was performed on the mud hydraulics. Both theoretical and field data show that density increase has, in such a case, a negative role on borehole stability while filtrate reduction and mud rheology enhancement are highly positive.

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Section: Introductionmentioning

confidence: 99%

Drilling Through Highly Fractured Formations: A Problem, a Model, and a Cure

1992

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Practical Advantages Of Mud Cooling Systems For Drilling

Maury

Guenot

1995

SPE Drilling &Amp; Completion

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Field cases studies of borehole stability showed that some failures were due to thermal effects, heating the upper part of open holes by mud circulation or reheating of the bottomhole when mud circulation cooling is stopped for instance. A complete analysis of the thermal regime in boreholes was performed and as a consequence, cooling of mud appeared as a mean to mitigate these effects. Series of tests were then carried out to check the practicality of installing such mud cooling systems. Many other advantages then appeared: decrease of the temperature of the borehole allowing better operation of the logging tools, better control of the mud rheology with less additives, extended use of MWD devices. But the most significant advantage is for the oil based suds which can be maintained at surface below their flash point, improving the safety of operations. The paper recalls and summarizes the results of observations, measurements and studies performed to determine the feasibility of such systems. Operational results are given for several field cases with emphasis on safety. The use of these very simple devices, which have been field proven on typical and 150C wells, is now contemplated for future HP-HT wells, INTRODUCTION AND BACKGROUND Till the beginning of 80's, little attention had been paid to the thermal effects in wellbores. Except in Russian literature, practical consideration had been given to mud temperature and mud cooling in the cases of geothermal drilling and drilling through Permafrost only. Nevertheless, thermal effects are commonly considered in mining and underground engineering, for heavy fuel oil storage and nuclear waste disposal. Some data are here recalled on the thermal effects in the wellbores. TEMPERATURE REGIME IN A WELLBORE WHILE DRILLING Even though this subject has been presented many times in the past, a good understanding of the temperature regime in a wellbore while drilling is not common in practice. This is mostly due to the lack of interest for this parameter, except in very specific cases such as mentioned above. Nowadays, PC software is easily available to provide a good estimate of the temperature profile in the well. At the same time, a larger access to the bottomhole temperature has been obtained through the use of MWD. When mud is circulated in a wellbore, a balance is reached between the different heat transfers. Bottomhole is cooler than the formation temperature, whereas top hole is warmer than the formation temperature. The amplitude of this deviation and also the temperature difference between bottom and top of the formation depend essentially of the mud flow rate. In turn, this depends on the borehole diameter, as the flow rate is usually decreased with the bit size. On fig.1, typical temperature profiles are given for the same wellbore for different drilling phases.

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