SU1675551A1 - Method for determination of rock strength during drilling - Google Patents

Abstract

FIELD: exploration drilling, m. used in areas of deep drilling for oil and gas. The goal is to increase the reliability of the hardness assessment of impermeable rocks. To do this, before lowering the bit to the bottom by number of nozzles in the bit at the wellhead, the weighted average diameter of the nozzles and their total area are determined. After the bit is lowered to the bottom, the rate at which the drilling fluid flows from these nozzles is measured. The hardness of impermeable rocks is determined by the mathematical p-le. Determination of rock strength in downhole conditions is based on a mathematical model that, in the criteria form, adequately reflects the dependence of the mechanical penetration rate on the parameters of the drilling and flushing mode.

Description

The invention relates to the process of deepening parametric, prospecting and exploration wells, associated with determining the strength (hardness) of rocks in the bottomhole conditions and can be used in areas of deep drilling for oil and gas.

The purpose of the invention is to increase the reliability of the evaluation of the hardness of impermeable rocks during well drilling.

The methods can be implemented in a more concise way.

The parameters of drilling and flushing are determined: axial load on the bit G, bit rotation frequency n, mud density p, bit diameter D, nozzle diameter dHi, weighted average nozzle diameter dH, mud flow rate.

Q, discharge rate from the bit nozzles Vn, О4

goon pressure pro. 4j

high VM penetration rate. Next, define

the strength of rocks is 7 ° under conditions (J

bottom hole by equation

f0 (Ј) (i ° l) «« yes «(-doi) 07S (| + 01Dр)

(D

.-one.

A is a constant dimensionless coefficient (A 2.5), where n is the bit rotation frequency, s

D - bit diameter, m;

G - axial load on the bit, N;

p is the density of the drilling fluid, kg / m;

Q - drilling fluid flow rate, m3 / s;

dH - weighted average nozzle diameter, m;

N - the number of nozzles in the bit, pcs;

S - total area of flushing holes in the bit, m

2

S n

7TdH

Vn

Vn - flow rate from bit nozzles, m / s,

Q. S

Pro - rock pressure, MPa at depth h;

Pr - hydrodynamic pressure of the mud column, MPa, density p at a depth h;

Рп - pore pressure, MPa, at depth h;

Гп - feather pressure gradient MPa / m;

AR - differential pressure, MPa,

DR R-Rl;

VM - mechanical penetration rate, m / s.

Formula (1) is obtained by converting the original equation

G h2GrUp P2 N0.43

U (2)

nD

D2 (Tn

02 (J

0.65

 0.2 ((Pro Pr) P2l0.72 0,

 (537) (& 1 CD)

relative to the hardness of the rocks Sto.

Equation (2) shows the dependence of the mechanical penetration rate on the parameters of the drilling mode (axial load on the bit G, bit rotation frequency n), bottom wash rate (flow rate Vn from nozzle bits nozzle diameter dH, mud flow rate Q) hardness of rocks in the downhole conditions of stpp, rock pressure Pro and bit diameter D.

The main dimensional complexes affecting the average mechanical speed of drilling include: specific mechanical / ™ h

high power (wkp) and hydraulic power in bit nozzles

.Vn2 D2

Q). Since the same

Since hydraulic power can be realized with multiple combinations of flow rate (Vn) and pump feed (Q), then Vn and Q values should generally be included in separate similarity criteria.

0

five

0

five

The assumed varying degree of influence of these criteria on the mechanical drilling rate and the dependence of the intensity of rock destruction on the contact surface of the direct action of the jetting jet necessitate the isolation of the average bit diameter (dH) in the corresponding similarity criteria.

In addition, the drillability of rocks is influenced by the difference between rock (Pro) and hydrodynamic (Pr) pressure, which should also be taken into account by a separate similarity criterion.

The set parameters are the following functional relationship:

, n, 0, -%, stp, p-Vn2, Q, (Pro-Pr), (3)

In accordance with the Buckingham l-theorem, expression (3) is transformed into a criterion dependence containing five dimensionless determining criteria for the similarity

  fi (wi .l & L5), (4)

Where

thirty

lz

Q

D3n

five

0

five

The dependence of the strength of clay rocks (stp) on the differential pressure AR (Pr - Pr) is shown by the equation

oh st0 (1 + CDR), (5)

where Hundred is the rock strength in the bottomhole conditions at AR 0, MPa;

K - dimensional coefficient, MPa (K to 0.1);

Pp - pore pressure, MPa.

Criterion equation (4) with regard to expression (5) is represented in power form

VM -b- (G a

.-. FOR D.2 //, I l «L G

nD OOA D2 (1 + 0.1 AP)

XjTf2-7G | 3

(6)

The exponents ai, 32as and the constant dimensionless coefficient A in equation (6) are determined by the least squares method when processing production data.

The coefficients of expression (6) are calculated by the rolling tolerance method on a computer.

As a result of identifying the coefficients of equation (6), a criterial generalized drillability model is obtained

Um -A. nD -2v

O2,4 D (1 + 0.1LR)

2.0

(7)

whereA (2,5) 2.

The outflow rate Vn is initially determined theoretically as the quotient of dividing the flow rate of drilling fluid Q by the total area of the flushing holes of the drill bit S. The value Q, the actual flow of the drilling pump, is known. The value of S is determined experimentally by measuring the diameter dHi of the 1st bit nozzle, calculating

its area by the formula Si

l: s1n1

and summing up these values

N

s 2 si,

i 1

where N is the number of bit nozzles, Thus

V - Q

Vn- -5.

After that, the calculated value Vn is refined by the results of hydraulic testing of the bit before lowering it into the well. To do this, drill the bit onto a square rod and pump drilling fluid through the bit with the same costs that drilling is planned for. In this case, the pressure P is measured using a pressure gauge in the injection line, and then the adjusted value Vn is obtained from the expression

, R

where c 0.9.

After the pumps stop, the chisel is turned away from the square rod, wrapped around the layout of the bottom of the drill string and lowered into the well for drilling.

Determining the strength of rocks in the downhole conditions is based on a mathematical model that, in the criteria form, adequately reflects the dependence of the mechanical penetration rate on the parameters of the drilling and flushing mode; The bit rotation frequency входит is included in this model in degrees less than one (0.8).

Claims (1)

Invention Formula The method of determining the strength of rocks in the process of posting wells, gg includes the measurement of mechanical ten 15 growth rate, axial load on the bit, bit rotation frequency, bit diameter, rock pressure differential over the bottomhole pressure, mud density, followed by calculating the strength of the drilled rocks, characterized in that, in order to increase the reliability of impermeable rocks hardness, The weighted average diameter of the nozzles and their total area is determined on the bottom by the number of nozzles in the bit at the wellhead, and after the bit is lowered to the bottom, the rate of mud flow is measured. ra of the nozzles, wherein the hardness of impermeable rock is determined from the expression 20 HX () "(-fv-o) ,; (i + oiApl m6 / Vl where A 2,5 is a constant dimensionless coefficient; n is the frequency of rotation of the bit, D - bit diameter, m; G - axial load on the bit, N; p is the density of the drilling fluid, kg / m; Q - mud flow rate, m / s;  - weighted average diameter of nozzles, m; S - total area of flushing holes in the bit; S n N - the number of bits in the bit, pieces; Vn - flow rate from bit nozzles, m / s: -§: Pro - rock pressure at depth h. Pa; Pr is the hydrodynamic pressure of the mud column at the bottomhole, with density p at depth h, MPa; Рп - pore pressure at depth h, MPa: Рп - Гп h; Гп - feather pressure gradient, MPa / m; DR - differential pressure, MPa; DR Pr-Pr; VM - mechanical penetration rate, m / s.