RU2185611C2 - Procedure determining rheological characteristics of drilling fluid in process of drilling - Google Patents

Abstract

FIELD: quality inspection while drilling holes for oil and gas. SUBSTANCE: mechanical drilling is stopped, starting effort is formed in hole while it is continued to be washed with change of flow rate of drilling fluid with simultaneous fixing of discharge pressure of drilling fluid in drill pipe string in correspondence with mathematical inequality. Obtained data are used to plot graph of dependence of discharge pressure of drilling fluid on flow rate of drilling fluid, straight line is extrapolated to crossing with coordinate axis of discharge pressure. Discharge pressure of drilling fluid is found by value of cut off segment. Value of discharge pressure is within limits of laminar mode of flow of drilling fluid. Weighted average of values of dynamic stress of displacement ( with due account of depth of hole ) and of plastic viscosity are found by mathematical formulas. EFFECT: increased accuracy and timeliness of determination of rheological characteristics in process of drilling. 2 dwg

Description

 The invention can be used in the process of quality control when drilling oil and gas wells.

Analysis of the existing level showed the following:
The rheological characteristics of the drilling fluid include dynamic shear stress τ _o and plastic viscosity η (see Bulatov A.I., Gabuzov G.G., Makarenko P.P. Hydromechanics of deepening and cementing wells. -M.: Publishing House Nedra ", 1999, p. 27).

 A known method for determining the viscosity of the drilling fluid during the drilling process, by which mechanical drilling and flushing of the well is stopped, create a straining force by lowering the drill string into the well, measure the time after the start of descent before the drilling fluid exits the well and determine η in the interval of the lowered string by mathematical formula (see AS 1244162 dated 06.22.84 according to class C 09 K 7/00, published in OB 26, 1986).

 The disadvantage of this method is the low accuracy of determining η, because the circulation of the drilling fluid is stopped, and the state of rest leads to an increase in the structure formation of the fluid, i.e. an increase in the static shear stress θ, which substantially distorts the value of the determined quantity. In addition, η is calculated every 30-40 m on average once every two days, i.e. intervalwise, and to obtain a weighted average value over the entire depth of the well, it is necessary to run the entire string, which requires significant time costs, in addition, the specified frequency of tripping operations reduces the speed of determination.

A known method for determining the dynamic shear stress of a drilling fluid during drilling, by which mechanical drilling and flushing of the well is stopped, create a straining force by lowering the drill string into the well, measure the time of the start of descent before the start of the flow of the drilling fluid from the well into the trench and the length of the runoff during this time drill pipes, and the value of τ _o is determined in the interval of the lowered string according to the mathematical formula (see AS 1035048 from 04/12/82, class C 09 K 7/00, published in OB 30, 1983).

The disadvantage of this method is the low accuracy of determining τ _o , because the circulation of the drilling fluid is stopped, and the quiescent state leads to an increase in the structure formation of the fluid, i.e. increasing the static shear stress θ, which significantly distorts the value of the determined value. In addition, τ _{o is} calculated every 30-40 m on average once every two days, i.e. intervalwise, and to obtain a weighted average value over the entire depth of the well, it is necessary to run the entire string, which requires significant time costs, in addition, the specified frequency of tripping operations reduces the speed of determination.

The technical result that can be obtained by carrying out the invention is as follows:
- increases the accuracy of determining the rheological characteristics of the drilling fluid during drilling due to the absence of the influence of thixotropic properties, as well as taking into account the actual thermobaric conditions and geometric features throughout the depth of the well;
- increases the efficiency of determination by reducing the time to determine the weighted average values of τ _o and η over the entire depth of the well, because in any case, the flushing time of the well with the necessary to determine less than the time of descent of the entire string of drill pipes.

где Q_min - минимальный расход бурового раствора, определяемый технической характеристикой насосного агрегата и обеспечивающий турбулентный режим течения бурового раствора в кольцевом пространстве скважины, м³/с;
Q_i - расход бурового раствора при i-м режиме промывки скважины, м³/с,
где i=1,...,k, при k≤n;
где n - максимальное количество вариантов подачи бурового раствора насосным агрегатом, определяемое его технической характеристикой;
Q_max - максимальный расход бурового раствора, определяемый технической характеристикой насосного агрегата и условием предотвращения поглощения бурового раствора, м³/с;
R₂, R₁ - средневзвешенные радиус скважины и наружный радиус бурильных труб, соответственно, м;
τ_{o лаб} - динамическое напряжение сдвига, определяемое в лабораторных условиях, Па;
ρ - плотность бурового раствора, кг/м³;
P_пг - давление поглощения, Па;
g - ускорение свободного падения, м/с²;
Н_пг - глубина залегания горизонта с минимальным давлением поглощения, м;
L_пг - длина бурильных труб до глубины залегания горизонта с минимальным давлением поглощения, м;
η_лаб - пластическая вязкость, определяемая в лабораторных условиях, Па•с,
и по полученным данным строят график зависимости давления нагнетания от расхода бурового раствора, экстраполируют прямую до пересечения с координатной осью давления нагнетания, по величине отсекаемого отрезка определяют давление нагнетания бурового раствора в колонне бурильных труб, значение которого находится в пределах ламинарного режима течения бурового раствора, причем определение средневзвешенной величины динамического напряжения сдвига проводят с учетом всей глубины скважины по формуле

где τ_o - средневзвешенная величина динамического напряжения сдвига, Па;
P_oн - давление нагнетания бурового раствора в колонне бурильных труб, значение которого находится в пределах ламинарного режима течения бурового раствора, Па;
L - длина бурильных труб, м;
R - средневзвешенный внутренний радиусы бурильных труб, м,
а также дополнительно рассчитывают средневзвешенную по глубине скважины величину пластической вязкости по формуле

где η - средневзвешенная по глубине скважины величина пластической вязкости, Па•с;
Р_нi - давление нагнетания бурового раствора в колонне бурильных труб при i-м установившемся режиме промывки скважины, Па.The technical result is achieved using the known method by stopping mechanical drilling, creating straining forces in the well and determining the weighted average value of the dynamic shear, in which creating straining forces is carried out by continuing to flush the well and changing the flow rate of the drilling fluid while fixing the injection pressure of the drilling fluid in the drill pipe string according to the inequality
Q _min ≤ Q _i ≤ Q _max
wherein

where Q _min is the minimum flow rate of the drilling fluid, determined by the technical characteristics of the pumping unit and providing a turbulent flow of the drilling fluid in the annular space of the well, m ³ / s;
Q _i - the flow rate of the drilling fluid at the i-th mode of washing the well, m ³ / s,
where i = 1, ..., k, for k≤n;
where n is the maximum number of drilling fluid supply options by the pump unit, determined by its technical characteristic;
Q _max - the maximum flow rate of the drilling fluid, determined by the technical characteristics of the pumping unit and the condition for preventing absorption of the drilling fluid, m ³ / s;
R ₂ , R ₁ - weighted average radius of the well and the outer radius of the drill pipe, respectively, m;
τ _{o lab} - dynamic shear stress, determined in laboratory conditions, Pa;
ρ is the density of the drilling fluid, kg / m ³ ;
P _PG - pressure absorption, Pa;
g is the acceleration of gravity, m / s ² ;
N _PG - the depth of the horizon with a minimum absorption pressure, m;
L _PG - the length of the drill pipe to the depth of the horizon with a minimum absorption pressure, m;
η _lab - plastic viscosity, determined in laboratory conditions, Pa • s,
and according to the data obtained, a graph of the dependence of the injection pressure on the flow rate of the drilling fluid is extrapolated, the line is extrapolated to the intersection with the coordinate axis of the injection pressure, the pressure of the drilling fluid in the drill pipe string, the value of which is within the laminar flow regime of the drilling fluid, is determined by the size of the cut-off section, determination of the weighted average value of the dynamic shear stress is carried out taking into account the entire depth of the well according to the formula

where τ _o is the weighted average value of the dynamic shear stress, Pa;
P _o - drilling fluid injection pressure in the drill pipe string, the value of which is within the laminar flow regime of the drilling fluid, Pa;
L is the length of the drill pipe, m;
R is the weighted average internal radius of the drill pipe, m,
and also calculate the average viscosity value over the depth of the well for the plastic viscosity according to the formula

where η - weighted average over the depth of the well, the value of plastic viscosity, Pa • s;
P _ni - the pressure of the injection of drilling fluid in the string of drill pipes at the i-th steady-state regime of flushing the well, Pa.

 A significant improvement in the technical and economic indicators of the well drilling process is facilitated by the rational choice of the hydraulic program, i.e., the regulation of hydrodynamic pressures due to controlled parameters (density and rheological characteristics of the drilling fluid, well flushing mode, etc.).

 First of all, the preparation of hydraulic programs is impossible without the correct determination of the rheological characteristics of drilling fluids (dynamic shear stress, plastic viscosity) and, therefore, hydraulic resistance during the circulation of fluids in a well being drilled. It is known that the rheological characteristics of most drilling fluids used are not invariant, as expected, due to the influence of thixotropic properties (static shear stress), which are not recorded when measuring with various types of viscometers, as well as with existing methods of determination directly in the well.

 A significant increase in the accuracy of determining the rheological characteristics of the drilling fluid is ensured by the absence of the influence of static shear stress, which is achieved under conditions of flushing the well with a steady flow of drilling fluid. In addition, the use of actual wellhead information when flushing the well when the bit is directly on the bottom (drilling fluid injection pressure in the drill string at the moment of steady flow, drilling fluid flow rate) allows us to solve the inverse problem, i.e., to determine the weighted average dynamic stress values shear, plastic viscosity of the drilling fluid, taking into account real thermobaric conditions and geometrical features (well and drill string design) throughout the depth of important.

в кольцевом пространстве

где Q - расход бурового раствора, м³/с;
Р_кп, Р_т - перепад давления в кольцевом пространстве и трубах, соответственно, Па;
Р_окп, Р_от - давление, необходимое для начала течения бурового раствора в кольцевом пространстве и трубах, соответственно, Па.According to the definition, dynamic shear stress and plastic viscosity quantitatively characterize the behavior of drilling fluids during their flow or deformation and are functions of shear rate. In drilling practice, drilling fluids are mainly used, the behavior of which can be described using the Bingham model. Buckingham equations describe the motion of Bingham fluids
in pipes

in the annular space

where Q is the flow rate of the drilling fluid, m ³ / s;
R _KP , R _t - pressure drop in the annular space and pipes, respectively, Pa;
P _okp , P _from - pressure required to start the flow of the drilling fluid in the annular space and pipes, respectively, Pa.

The creation of straining forces directly in the borehole by circulating the drilling fluid makes it possible to determine the pressure P _n , which is proportional to the pressure required to start the flow of the drilling fluid in the drill pipes and the annular space of the borehole. For this purpose, the dependence of the drilling fluid injection pressure in the drill string is used, as the sum of the hydraulic pressure losses in the pipes and the annular space of the well, on the flow rate of the drilling fluid, obtained from the results of actual measurements at different modes of well flushing. The flushing regimes are determined by specific geological and technical conditions: the technical characteristics of the pumping unit, ensuring a turbulent flow regime and preventing the absorption of drilling fluid.

Figure 1 shows the dependence of the injection pressure of the drilling fluid in the drill string at the moment of steady flow from the flow rate of the drilling fluid. In the region of low flow rates of the drilling fluid, the graph has a noticeable curvature and corresponds to the laminar flow regime (section 1); obtaining a linear dependence in the region of high flow rates indicates the absence of a plastic flow core in the fluid flow and corresponds to the turbulent flow regime of the drilling fluid (section 2). To obtain a linear relationship, two well flushing modes are sufficient (Q _min , Q _max ). After approximating the data of the linear section of the curve by the least squares method, it is necessary to extrapolate the linear section to the intersection with the coordinate axis of the discharge pressure. The intersection point corresponds to the beginning of the flow of the drilling fluid, i.e., at a higher pressure P _{, the} flow rate of the drilling fluid is non-zero. The error of such an approximation decreases with the growth of the rectilinear portion of the curve and is less than 6%.

It should be noted that it is unacceptable to use the actual data when flushing the well with a flow rate below Q _min , which corresponds to the laminar flow regime of the drilling fluid, because the method used to determine the pressure required to start the flow of the drilling fluid becomes illegal. At a flow rate in excess of Q _max , mud is absorbed.

а также решать их относительно перепадов давления. При графическом методе решения задачи по величине отсекаемого участка определяют давление, пропорциональное давлению, при котором начнется течение бурового раствора в трубах и в кольцевом пространстве, т.е. расход бурового раствора равен нулю:

Учитывая, что динамическое напряжение сдвига бурового раствора в трубах равно динамическому напряжению в кольцевом пространстве

определяют давления, необходимые для начала течения в трубах

и в кольцевом пространстве

Подставляя полученные значения давлений, необходимых для начала течения бурового раствора, в формулы динамического напряжения сдвига τ_o, вычисляют его средневзвешенную величину.Using linearization allows us to simplify Buckingham equations by

and also to solve them regarding pressure differences. In the graphical method of solving the problem, the pressure proportional to the pressure at which the flow of the drilling fluid in the pipes and in the annular space begins, is determined by the size of the cut-off section, i.e. mud flow rate is zero:

Given that the dynamic shear stress of the drilling fluid in the pipes is equal to the dynamic stress in the annular space

determine the pressure required to start the flow in the pipes

and in the annular space

Substituting the obtained pressure values necessary to start the flow of the drilling fluid into the dynamic shear stress formulas τ _o , calculate its weighted average value.

Considering that the drilling fluid injection pressure in the drill string is equal to the sum of the hydraulic pressure losses in the pipes and the annulus determined from the simplified Buckingham equation, the weighted average value of the drilling fluid plastic viscosity η is calculated.
An analysis of the inventive step showed the following: there is a known method for determining θ from the injection pressure in drill pipes during restoration of circulation (see McCray A.U. and Kole F.U. Oil drilling technology. M., Gostoptekhizdat, 1963, pp. 326-329 ); known laboratory method for determining τ _o and η by the pressure drop between the ends of the pipe and the flow rate of the drilling fluid, providing a turbulent flow regime, taking into account the Buckingham equation (see Macovey N. Hydraulics of drilling. Trans. from room. - M .: Nedra, 1986, p. 198-199). Based on the foregoing, we have not identified technical solutions that are based on features that match the distinctive features of the claimed technical solution. Thus, the latter does not follow explicitly from the analyzed prior art, i.e. has an inventive step.

 In more detail, the essence of the proposed method is illustrated by the following example.

Example. The reservoir is represented by sandstones of the Valanginian deposits, well 12 of the Yuzhno-Parusnaya gas condensate field. A Uralmash 3D-76 drilling rig and a U8-7M pump with cylindrical bushings with a diameter of 200 mm are used, which, with a fill factor of 0.9, creates n = 6 drilling fluid supply options: flow rate 0.028 m ³ / s at 40 double strokes in 1 min; 0.031 m ³ / s - 45; 0.035 m ³ / s - 50; 0.038 m ³ / s - 55; 0.042 m ³ / s - 60; 0.045 m ³ / s - 65.

Initial data:
The bottom hole depth N, m - 3200
Depth of bed with a minimum absorption pressure N _pg , m - 2300
Absorption pressure P _pg , MPa - 28.05
The weighted average radius of the well R ₂ , m - 0,110
The weighted average outer radius of the drill pipe R ₁ , m - 0,063
Weighted average inner radius of drill pipes R, m - 0,054
The density of the drilling fluid ρ, kg / m ³ - 1200
Dynamic shear stress determined in laboratory conditions τ _olab , Pa - 3.6
The plastic viscosity determined in laboratory conditions η _lab , Pa • s - 0.02
Mechanical drilling is stopped at a depth of 3200 m, while continuing to flush the well with a drilling fluid flow rate of 0.031 m ³ / s, the injection pressure in the drill string is fixed at 5.0 MPa.

и максимальный расход бурового раствора, определяемый предотвращением поглощения бурового раствора

С учетом технических возможностей насосного агрегата создают k=3 режима промывки скважины, последовательно меняя расход раствора.Determine the minimum flow rate of the drilling fluid, providing a turbulent flow regime in the annular space of the well

and maximum mud flow rate determined by preventing mud absorption

Taking into account the technical capabilities of the pumping unit, k = 3 well washing regimes are created, sequentially changing the flow rate of the solution.

The first mode of flushing the well corresponds to the estimated minimum flow rate and equal to Q _i = 0.035 m ³ / s, while the pressure of the injection of drilling fluid into the drill string P _n1 = 5.4 MPa. Next, the well is washed in the second mode at Q ₂ = 0.038 m ³ / s, while P _n2 = 5.7 MPa and the well is washed in the third mode, corresponding to the estimated maximum flow rate and equal to Q ₃ = 0.042 m ³ / s at P _n3 = 6.0 MPa.

According to the data obtained, a graph of the dependence of the injection pressure on the flow rate of the drilling fluid, shown in Fig.2. The straight line is extrapolated to the intersection with the coordinate axis of the discharge pressure. The magnitude of the cut-off segment determines the injection pressure of the drilling fluid in the drill pipe string, the value of which is within the laminar flow regime of the drilling fluid, P _it = 2.5 MPa.

и рассчитывают средневзвешенную по глубине скважины величину пластической вязкости по формуле:

Сравнивают фактические значения τ_o и η с лабораторными τ_oлаб и η_лаб. Точность определения увеличилась в 2-2,5 раза.The weighted average value of the dynamic shear stress is determined taking into account the entire depth of the well by the formula

and calculate the weighted average over the depth of the well, the value of plastic viscosity according to the formula:

Compare the actual values of τ _o and η with laboratory τ _olab and η _lab . The accuracy of determination increased by 2-2.5 times.

 Determining the rheological characteristics of the drilling fluid according to wellhead information during the flushing process increases the safety and quality of drilling by ensuring the required bottomhole pressure, reducing the likelihood of complications and accidents associated with clogging of the bore, mudding of the reservoir, fluid manifestations and absorption of the drilling fluid, as well as fulfilling restrictions pressure changes in the well during flushing, tripping operations.

Claims (1)

A method for determining the rheological characteristics of a drilling fluid during drilling by stopping mechanical drilling, creating straining forces in the well and determining a weighted average value of the dynamic shear stress, characterized in that creating straining forces is carried out by continuing to flush the well and changing the flow rate of the drilling fluid while recording the drilling pressure solution in the drill string according to the inequality
Q _min ≤Q _i ≤Q _max ,
wherein

where Q _min is the minimum flow rate of the drilling fluid, determined by the technical characteristics of the pumping unit and providing a turbulent flow of the drilling fluid in the annular space of the well, m ³ / s;
Q _i is the flow rate of the drilling fluid during the i-th flushing mode of the well, m ³ / s, where i = 1,. . . , k, for k no more than n; where n is the maximum number of drilling fluid supply options by the pump unit, determined by its technical characteristic;
Q _max - the maximum flow rate of the drilling fluid, determined by the technical characteristics of the pumping unit and the condition for preventing absorption of the drilling fluid, m ³ / s;
R ₂ , R ₁ - weighted average radius of the well and the outer radius of the drill pipe, respectively, m;
τ _0lab - dynamic shear stress determined in laboratory conditions, Pa;
ρ is the density of the drilling fluid, kg / m ³ ;
R _PG - pressure absorption, Pa;
g is the acceleration of gravity, m / s ² ;
N _PG - the depth of the horizon with a minimum absorption pressure, m;
L _PG - the length of the drill pipe to the depth of the horizon with a minimum absorption pressure, m;
η _lab - plastic viscosity, determined in laboratory conditions, Pa • s,
and according to the data obtained, a graph of the dependence of the injection pressure on the flow rate of the drilling fluid is extrapolated, the line is extrapolated to the intersection with the coordinate axis of the injection pressure, the pressure of the drilling fluid in the drill pipe string, the value of which is within the laminar flow regime of the drilling fluid, is determined by the size of the cut-off section, determination of the weighted average value of the dynamic shear stress is carried out taking into account the entire depth of the well according to the formula

where τ ₀ is the weighted average value of the dynamic shear stress, Pa;
P _he - the pressure of the injection fluid in the drill string, the value of which is within the laminar flow regime of the drilling fluid, Pa;
L is the length of the drill pipe, m;
R is the weighted average inner radius of the drill pipe, m,
and also calculate the average viscosity value over the depth of the well for the plastic viscosity according to the formula

where η - weighted average over the depth of the well, the value of plastic viscosity, Pa • s;
P _ni - the pressure of the injection of drilling fluid in the string of drill pipes at the i-th steady-state regime of flushing the well, Pa.

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