RU2256762C1 - Method for incompetent mud shale bed penetration during drilling operation - Google Patents

Abstract

FIELD: oil and gas well drilling, particularly to penetrate incompetent mud shale bed.

SUBSTANCE: method involves performing subdrilling by chisel within the boundaried of bed consisting of incompetent mud shale with the use of visco-plastic drill fluid circulating in annular well bore cavity. Drill fluid flow is within laminar regime. To provide guaranteed laminar drill fluid flow and, therefore, to provide penetration of above bed without well wall caving the selected flow rate of drill fluid Q is 20-30% less than critical flow rate Q_cr corresponding to transition from laminar regime to turbulent one. The selected visco-plastic drill fluid must have minimal possible filtration efficiency.

EFFECT: prevent well erosion and well wall caving during incompetent mud shale bed drilling.

Description

The invention relates to the field of drilling oil and gas wells, and in particular to methods of preventing erosion destruction and subsequent formation of caverns in the walls of the wells when drilling intervals of the formation with unstable clay rocks.

It is known that the stability of well walls composed of clay rocks is influenced by many factors [1], [2], such as clay mineralogy, physicochemical and rheological properties of the drilling fluid, osmotic processes, hydrodynamic pressure factors of the wash fluid column.

The violation of the stability of clay rocks is accompanied, as is known, by complications of the wellbore, collapses and caverns. The presence of caverns, especially between oil and aquifers, reduces the quality of their separation, is the reason for the influx of water during the initial development, as well as the reason for the increase in the percentage of water cut in the formation during the operation of the well. Caverns are mainly formed during the sinking of unstable clay rocks - shales of the Verey, Tula, Bobrikov, Kyn, and Shash horizons due to erosion destruction by a turbulent flow of washing fluid. They lead to complications - multiple studies of the trunk and sticking of the drilling tool. So, when attaching the well, the density of the cement in the cavity interval decreases from 1850 to 1300 kg / m ³ . Cement stone from such a solution cannot serve as a reliable support for the annular channel. This leads to serious accidents in the well accompanied by collapse of the production string and its sticking, especially in the interval of Kyn clay.

A known method of drilling wells with unstable clay rocks without caverning [3], including deepening the wellbore with a bit in the interval of the formation with unstable clay rocks using a viscoplastic flushing fluid in a laminar flow regime in the annular channel of the wellbore.

The known method in its technical essence and the achieved result is closer to the proposed one and can be adopted as a prototype.

However, as the practice of drilling unstable clay rocks shows, the critical velocity V _cr , at which the transition from the laminar flow regime to turbulent occurs, is difficult to control, and in some cases impossible, since in difficult borehole conditions there is a change in the plastic viscosity of the drilling fluid, dynamic shear stress . Therefore, it is necessary to constantly make adjustments in order to restore its rheological characteristics. Therefore, the method described in the prototype does not provide a guaranteed laminar flow regime in the annular channel of the well when a bit is drilled with the mentioned interval of the formation with unstable clay rocks.

In [3], it was noted that it is possible to control the flow regime, rheological parameters of viscoplastic drilling fluids during the passage of unstable clay rocks at various flow rates of flushing fluid, and to achieve a laminar flow regime in the annular channel of the wellbore.

As a result of many years of research, the authors developed a technology for drilling intervals of unstable clay rocks by drilling without caverning at a flow rate of the flushing fluid, which ensures a guaranteed laminar flow regime.

The technical task of the present invention is the drilling of unstable clay rocks with washing the wellbore with a flow of drilling fluid, providing a guaranteed laminar flow regime of a viscoplastic drilling fluid in the annular channel, therefore, without caverning, i.e. without erosive destruction of the borehole walls and subsequent formation of caverns there.

The problem is solved by the described method, including deepening the well with a bit in the interval of the formation with unstable clay rocks using a viscoplastic flushing fluid in a laminar flow regime in the annular channel of the wellbore.

What is new is that to ensure a guaranteed laminar flow regime in the annular channel of the wellbore, and therefore, to drill a bit of the above-mentioned interval without caverning, the flow rate (Q) of the flushing fluid is chosen 20-30% less than the critical flow rate (Q _cr ), at which change of the laminar regime to turbulent, while the viscoplastic washing liquid is chosen with the lowest possible filter recovery. Thus,

Q = 0.8 ÷ 0.7 Q _cr ,

where Q is the flow rate of the flushing fluid, providing a guaranteed laminar flow regime in the annular channel of the well, l / s;

Q _kp is the critical flow rate of the flushing fluid at which the laminar flow regime changes to turbulent, l / s.

It is known that the critical flow rate (Q _cr ) of the washing liquid is determined from the following mathematical expression:

Q _cr = 1000V _cr · F, (1)

where V _kp is the critical velocity corresponding to the transition from the laminar to turbulent regime, m / s;

F is the area of the annular channel, the wellbore, m ² .

The critical velocity V _cr is determined from the following expression:

V _cr = η Re _cr / ρ (d _c -d _t ), (2)

Where

Re _cr = 7.3 Not ^0.58 +2100, (3)

Where

He = τ ° ρ d ² / η ² , (4)

where d is the hydraulic diameter, m, d = d _c -d _t ;

d _c - bit diameter (wells), m;

d _t is the outer diameter of the over-bit pipe, m;

τ ° - dynamic shear stress, dPa;

η — plastic viscosity, dPa · s;

ρ is the density of the drilling fluid, kg / m ³ .

The method is as follows.

First, preparatory work is carried out, namely, that at the drilled well, intervals of unstable clay rocks of the developed oil or gas reservoir are revealed from previously drilled wells or exploratory drilling wells. Then, taking into account the data obtained, a viscoplastic polymer clay or polymer clay clay drilling mud (flushing fluid) is prepared with the minimum possible filter recovery, using salt-resistant polymers, for example, Proestol 2540 or Accotrol S-622, etc., with a density of 1200-1400 kg / m ³ .

Then, taking into account the rheological characteristics of the obtained drilling fluid, its density, the area of the annular channel of the wellbore, as noted above by the formula (1) and using formulas (2), (3) and (4), the critical flow rate Q _{cr of the} drilling fluid is determined .

According to the invention proposed for protection by a patent, the flow rate of the washing fluid Q, which ensures a guaranteed laminar flow regime in the annular channel of the well when driving the interval of unstable clay rocks - shales, is determined as follows:

Q = 0.8-0.7 Q _cr , (5)

where Q is the flow rate of the flushing fluid, providing a guaranteed laminar flow regime in the annular channel of the well, l / s;

Q _kp is the critical flow rate of the flushing fluid at which the laminar flow regime changes to turbulent, l / s.

In the process of drilling a well at the wellhead, the flow rate Q of the flushing fluid is constantly monitored using known flow meters for compliance with the above equality [5].

The method was tested in the field when drilling wells No. 30406, 24686, 24755, 6943 “3”, 26782 “3”, 6300 “3”, 2120 “3”, at the opening of the Kynovsky horizon.

The test results showed the high efficiency of the technology proposed for patent protection. Well penetration in the listed intervals of unstable clay rocks was carried out without complications and cavern formation.

The technical and economic advantage of the invention is as follows.

Using the proposed method provides the drilling intervals of unstable clay rocks by drilling without caverning, therefore, without complications and sticking of the drilling tool, which positively affects the drilling performance. Ultimately, the exclusion of cavity formation in the walls of the well leads to an increase in the quality of formation separation, which in turn eliminates the influx of water during the initial development of the well, reduces the percentage of water cut during operation and eliminates accidents associated with crushing of the production string, for example, in the Kynov clay. In addition, cement consumption is reduced when cementing a production casing.

Sources of information

1. The book of Mikheev VL “Technological properties of drilling fluids”, M., Nedra, 1979

2. The journal “Oil industry”, No. 12, 2000, pp. 128-132, article by T. N. Bikchurin, I. G. Yusupov and R. S. Gabidullin and others. “Study of technical and technological factors determining the stability of the Kynovsky argelites during well drilling. ”

3. The journal “Oil industry”, No. 4, 2001, p. 26, article by T. N. Bikchurin, I. G. Yusupov and R. S. Gabidullin “Study of the influence of various factors on the mode of flow of the drilling fluid through the annular channel the borehole ”[prototype].

Claims (1)

A method of driving unstable clay rocks while drilling oil and gas wells, for example shale, comprising deepening a well with a bit in the interval of a formation with unstable clay rocks using a viscoplastic flushing fluid in a laminar flow regime in the annular channel of the wellbore, characterized in that, to ensure guaranteed laminar flow regime in the annular channel of the wellbore, and therefore, with a bit of the aforementioned interval without drilling, (Q) the washing liquid is chosen 20 ÷ 30% less than the critical flow rate (Q _cr ), at which the laminar regime changes to turbulent, while the visco-plastic washing liquid is chosen with the lowest possible filter recovery.