Wells – Processes – Cementing – plugging or consolidating
Patent
1990-08-02
1991-07-16
Britts, Ramon S.
Wells
Processes
Cementing, plugging or consolidating
166387, 166207, 166287, E21B 3300
Patent
active
050316990
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to methods of welldrilling, and more particularly it relates to a method of casing off a producing formation in a well.
The invention can be employed to the utmost effect for protection of a producing formation against pollution by the flushing fluid and cement slurry when running casing in the well (casing-in process).
In the process of well-drilling and casing-in, the borehole fluids including the flushing fluid and the cement slurry find their way into a producing formation, adversely affecting its reservoir properties, which prolongs the well completion period, and involves additional work on restoring the reservoir properties of the formation, incurring extra labor and material inputs and increased costs of the associated equipment and the use transport facilities.
PRIOR ART
There is known a method of casing off a producing formation in a well, including drilling into the producing formation, running in a flow casing string, cementing the latter above the producing formation and perforating the uncemented portion of the flow casing string in the pay sesction, i.e. in the producing formation zone, thus re-exposing the producing formation (Yu. V. Vadetski, "Drilling oil and gas wells", 1973 , Nedra/Moscow/, pp. 346-348).
A serious drawback of this method is that it fails to ensure reliable isolation of the producing formation from the underlying strata, as the cementing of the casing string is carried out above the producing formation.
Another shortcoming of the known method is its unsuitability in cases where the producing formations display a tendency towards caving-in, as this involves the filling of the annulus between the flow casing string and the producing formation by caved-in rock, which impairs the filtration of the product from the formation.
There is further known a method of casing off a producing formation in a well (SU,A, No. 911015), including the steps of drilling into the formation and perforating it, casing it off with a fluid-impervious envelope of profile pipes which are reamed in the course of their setting by building up a pressure drop the reacross, and running through them and cementing a flow casing string of a smaller diameter in comparison with the target diameter, followed up by the re-exposure of the producing formation.
A major drawback of this method of the prior art is the increased thickness of the isolating layer formed by the walls of the fluid-impervious envelope and of the flow casing string, and by the cement ring therebetween, which complicates the re-exposure of the formation and impairs the efficiency of the filtration of the product from the formation into the well. The setting of the flow casing string of a reduced diameter decreases the filtration area of the formation and thus brings down the yield of the well. Furthermore, the method of the prior art involves additional pulling and running-in operations of setting up the fluid-impervious envelope, which incurs extra inputs of time, materials and labor.
The present invention has for its object the creation of a method of casing off a producing formation in a well, providing for increasing the area of filtration while at the same time reducing the thickness of the isolating layer separating the producing formation from other formations.
DISCLOSURE OF THE INVENTION
This object is attained in a method of casing off a producing formation in a well, including the steps of drilling into the producing formation, shutting off the producing formation with a fluid-impervious envelope of profile pipes which are reamed in the process of their setting by building up a pressure drop thereacross, running in and cementing a flow casing string, and re-exposing the producing formation, in which method, in accordance with the present invention, the borehole is reamed in the producing formation zone prior to the setting of the impervious envelope, and the running-in of the flow casing string is terminated after the string enters the upper part of the impervious envelope.
The
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Yu. V. Vadetski, "Drilling oil and gas wells", 1973, Nedra/Moscow, pp. 346-348.
Neftyanoe khozyaistvo, N4, Apr. 1982, Nedra, Moscow, G. S. Abdrakhmanov et al., "Isolation of Absorption Zones with Steel Pipes Without Diminishing the Well Diameter", pp. 26-28.
Abdrakhmanov Gabdrashit S.
Artynov Vadim V.
Fatkullin Rashat K.
Filippov Vitaly P.
Ibatullin Rustam K.
Britts Ramon S.
Schoeppel Roger J.
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