RU2213840C2 - Method of borehole desludging - Google Patents

Abstract

FIELD: hole drilling. SUBSTANCE: method includes hole washing with mud with rotation and reciprocating of drill stem assembly with eccentrics. Borehole is cleaned from sludge by lifting drill stem assembly at depths with distance between them determined by length of drill stem assembly with eccentrics plus length of working rod for time required for carrying-out of sludge to surface with mud flow from interval of residence of said assembly with eccentrics. In borehole sections with zenith angle up to 15- 20 deg., washing of borehole is carried out within intervals of caverns. In inclined and horizontal sections of borehole, washing with mud is effected from hole bottom to depth at which zenith angle becomes less than 15-20 deg. EFFECT: higher efficiency of cleaning of inclined, horizontal and cavernous sections of boreholes.

Description

 The invention relates to the field of well drilling.

 A known method of cleaning a wellbore from sludge by flushing it through a string of drill pipes pacing within the length of the lead pipe, wherein the upward velocity of the flushing fluid in the annular space of the well should be at least 1.0 m / s. Duration of flushing - at least two cycles of circulation [1].

 The disadvantage of this method is the poor cleaning of caverns and places where the pipe string is adjacent to the wall of the well, because providing a flow rate of flushing fluid of at least 1.0 m / s in the indicated intervals is practically impossible in many cases.

 As a result, the accumulation of sludge occurs in the well, which can be the reason for the absorption of the drilling fluid, sticking of the drilling tool and poor quality cementing of the well.

 The closest in technical essence and the achieved result to the proposed method is the method [2], in which several eccentric deflectors (eccentric) are installed in the drill pipe string above the weighted drill pipes (UBT) [3]. With simultaneous rotation and longitudinal displacements, the drill pipe string transversely moves in the borehole in the eccentric location interval, as a result of which annular fluid flows throughout the annular section without the formation of stagnant zones, thereby causing efficient transport of cuttings even at low, less than 1, 0 m / s, upstream speeds.

 The disadvantage of this method is that in the intervals of the borehole located above the position of the arrangement with the eccentrics and characterized by the presence of cavities and the fit of the drill pipe string to the borehole wall (sections of the inclined and horizontal boreholes), the conditions for the removal of cuttings are worsened.

 Experimental studies have established and field studies have confirmed [4] that, due to the Boycott effect in deviated wells in suspensions that are both at rest and in motion, the solid phase settles towards the bottom wall of the well. With regard to drilling fluids, this effect is manifested primarily in the sedimentation of sludge. The deposition process is intensified in places where the flow rate decreases, namely in caverns, narrowed parts of the annular section due to the eccentric position of the column in the well.

 This means that after removal of the sludge from the work zone by the eccentric arrangement, conditions again appear for this sludge to fall onto the well walls.

 The aim of the invention is to increase the efficiency of cleaning cavernous, inclined and horizontal sections of the trunk from sludge.

This goal is achieved by the fact that the well is flushed with the solution during rotation and pacing of the eccentric assembly, when the assembly is lifted at depths, the distance between which is determined by the eccentric assembly length plus the working rod length, during the time required for the sludge to be transported to the surface by the solution flow from the interval finding layouts with eccentrics. Moreover, in sections of the wellbore with an zenith angle of up to 15-20 ^o, washing with the solution of the wellbore is carried out in the intervals of caverns, and in inclined and horizontal sections of the wellbore, washing with the solution is carried out from the bottom to a depth at which the zenith angle becomes less than 15-20 ^o .

 The essence of the method.

A drill pipe string with eccentrics (at least two) installed at a distance of 25-37 m from each other is lowered to the lower boundary of the interval to be cleaned of sludge. When the drill pipe string is rotated at a speed of 10-70 ¹ / s and paced within the length of the lead pipe, the well is washed for the time necessary for the sludge to flow out of the solution from the pacing interval of the assembly with eccentrics. After that, the drill pipe string is lifted to the length of the eccentric arrangement and the flushing is repeated again. In wells with zenith angles of up to 15–20 ^{o, the} barrel is flushed in the intervals of caverns, and in deviated and horizontal wells, flushing is carried out from the bottom to the depth at which the zenith angle of the well becomes less than 15–20 ^o .

 Example. The implementation of the proposed method will be considered on a practical example of cleaning an inclined section of the trunk in the range of 900-1900 m, complicated by cavities and gutters. The main information on the well is presented in the table.

 To a depth of 900 m, the well was cased with a 324 mm column.

Previously, an operation was performed to clean the well from sludge using a portion of 10 m ^{3 of} increased viscosity of the drilling fluid with a density of 1700 kg / m ³ at a density of the solution in the well of 1230 kg / m ³ . The removal of sludge was 1 m ³ .

 To clean the well by the proposed method, the following layout was used: guide plug with a diameter of 202 mm + drill pipe 127 mm x 12.6 m + spiral centralizer 289 mm + pipes 127 mm x 25.3 m + eccentric (E) diameter 282 mm + pipes 127 mm x 25.2 m + E285 mm + pipes 127 mm. Layout length - 53 m.

When the assembly was lifted from a depth of 1900 m, washing was carried out every 52 m for 5-10 minutes with pump supply of 43 l / s, as well as walking the assembly to the length of the working rod (14 m) and the rotor speed of 72 rpm. At a depth of 900 m, the well was washed for 60 minutes. Removal of sludge was 3.0 m ³ , i.e. 3 times more than in the previous operation.

 The efficiency of cleaning inclined, horizontal and cavernous sections of the wellbore is significantly increased, because when washing during the rise, re-contamination of the well with sludge is completely prevented.

Sources of information
1. Typical instructions for the safety of oil and gas wells. // Typical safety instructions for the construction of oil and gas wells. Book 1. Gosgortekhnadzor of Russia, M., 1996, p. 2.2.3.

 2. Kushnarenko N.A., Babayan E.V., Kobzev V.A. The use of drill eccentric type EB. "Oil industry", 8, M .: Nedra, 1978. - prototype.

 3. Hanson H., Trigg T., Rachal G., Zammora M. Investigation of Barite Sag in Weighted Drilling Fluids in Highly Deviated Wells // SPE paper 20423 presented at the SPE Annual Conference and Exhibition, - New Orlean, 1990 - Sept . - p 23-26.

Claims (1)

A method of cleaning a wellbore from sludge, including flushing a well with a solution during rotation and pacing of an eccentric arrangement, characterized in that washing a well with a solution during rotation and pacing of an eccentric arrangement is performed when the assembly is lifted at depths, the distance between which is determined by the length of the eccentric arrangement plus length the working rod, during the time necessary for the removal of sludge to the surface by the flow of the solution from the interval of finding the layout with eccentrics, and in areas the borehole with an zenith angle of up to 15-20 ^° rinse with a solution of the borehole in the intervals of caverns, and in inclined and horizontal sections of the borehole, the rinse with a solution is carried out from the bottom to a depth at which the zenith angle becomes less than 15-20 ^o .

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