RU2810364C1 - Method for hydrodynamic diagnostics of open hole of well under construction - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to the methods for hydrodynamic examination of a wellbore during the drilling process. A method for hydrodynamic diagnostics of an open wellbore under construction includes determining the injectivity coefficient of its walls by injecting flushing fluid into the well while controlling the pressure and fluid flow rate in the well-rock system. Determination and registration of the injectivity coefficient of the well walls is carried out during continuous mechanical drilling, without stopping to examine the well and without a packer, obtaining graphical and digital data of the injectivity coefficient of the well walls and the dependence of the flow rate of fluid pumped into the well from pressure in real time, by dividing the wellbore wells into micro-intervals, in which the flushing parameters and depth change slightly compared to the length of the well, and taking into account micro-changes in the injectivity coefficient when passing through the next such micro-interval. The microchange in the injectivity coefficient during the passage of the next such microinterval is calculated using certain dependencies. Complete and reliable data on absorbent formations and the hydrodynamic characteristics of the wellbore under construction are received, the success rate is increased and the time and money spent for these works are reduced.

EFFECT: improving the quality, reliability and durability of the well, therefore, an increase in its operational capabilities and an increase in production are expected.

1 cl

Description

The invention relates to the field of oil and gas industry, namely, to methods for hydrodynamic examination of a wellbore during the drilling process.

There is a known method for hydrodynamic diagnostics of the wellbore under construction (Regulations for isolating lost circulation zones, preparing and assessing the wellbore for casing, RD 153-39.0-590-08, Bugulma, 2008), including the study of lost circulation formations through blowout preventer equipment (BOP) by injection into the well drilling fluid using a drilling pump or cementing unit with a closed air barrier, measuring the corresponding values of pressure and injection performance and obtaining the injectivity coefficient of the absorption zone by calculation.

The disadvantage of this method is that the method is approximate and evaluative and is not intended to obtain the hydrodynamic parameters of specific formations along the wellbore with registration of their occurrence intervals. The losses of the drilling fluid are measured simultaneously over a significant interval penetrated by drilling, therefore large errors in the obtained results of hydrodynamic studies are inevitable.

There is a known method for hydrodynamic diagnostics of a wellbore under construction (Regulations for isolating lost circulation zones, preparing and assessing a wellbore for casing, RD 153-39.0-590-08, Bugulma, 2008), including determining the injectivity coefficient of the well walls during an interval study by injecting flushing fluid into the well fluids in various modes while controlling pressure and fluid flow using cementing units and hydromechanical packers.

The disadvantage of this method is the receipt of only discrete data from studies of the hydrodynamic parameters of the wellbore, which are carried out at depths limited in number, errors in measurements due to the difficulty of isolating a single formation from neighboring sections of the wellbore, also composed of permeable rocks, and the influence of the subjective (“human”) factor , which makes it impossible to adequately mathematically interpolate the obtained data.

The closest in technical essence is the method of hydrodynamic diagnostics of the trunk of a well under construction (Technical instructions for conducting geological and technological studies of oil and gas wells, RD 153-39.0-069-01, Tver, 2001), including geological and technological studies (GTI) using automated control of technological parameters and obtaining long-term data, including pressure and flow rate of the flushing fluid at the well inlet and flow rate at the well exit using sensors interacting via a communication channel with the control module.

The disadvantage of this method is that GTI, when recording the intervals of gas and oil shows or absorption of the flushing fluid and their intensity, does not allow measuring the injectivity coefficient of absorption zones and other sections of the wellbore.

The technical task is to carry out hydrodynamic diagnostics of the open hole of a well under construction by determining and recording the injectivity coefficient of its walls, including absorption zones, during the deepening of the well continuously, without stopping to study the well and without a packer.

The technical problem is solved by hydrodynamic diagnostics of an open wellbore under construction, which includes determining the injectivity coefficient of its walls by injection of flushing fluid into the well while controlling the pressure and flow rate of the liquid in the well-reservoir (rock) system.

What is new is that the determination and registration of the injectivity coefficient of the well walls is carried out in the process of continuous mechanical drilling, without stopping to study the well and without a packer, with obtaining graphical and digital data of the injectivity coefficient of the well walls and the dependence of the flow rate of fluid pumped into the well from pressure in real mode time, by dividing the trunk into micro-intervals and taking into account micro-changes in the injectivity coefficient when passing through the next micro-interval.

The method is carried out in the following sequence.

The process of deepening a well is divided into small amounts of shaft penetration - microintervals. This is a very small, but realistic well interval, where the flushing parameters and depth vary slightly compared to the length of the well. At the same time, the higher the sensitivity and lower the error of the devices, the higher the accuracy of calculating the pickup coefficient and the smaller the microinterval.

In the process of mechanical drilling of a well, a graph is drawn of changes in the injectivity coefficient of the walls of the open wellbore during its deepening at low (working) pressures. A hydrodynamic study at these low pressures is sufficient to determine and record the injectivity coefficient of the well walls, including fixing the beginning and end (top and bottom) of absorption zones and identifying undesirable intensity of the onset of absorption. To do this, through each micro-interval of shaft penetration, micro changes are recorded: the flow rate of the drilling fluid at the outlet, penetration, bottomhole pressure (the sum of hydrostatic pressure and pressure losses), and, having already real numbers, by calculation using the formula below, a specific point on the graph is obtained. In this case, this will be a discrete point corresponding to a microchange in the injectivity coefficient during the accepted penetration value. From periodically obtained, calculated and recorded on the graph, through each microinterval traversed by the bit, discrete points are obtained by interpolation, an almost continuous geophysical curve of changes in the injectivity coefficient along the wellbore. Along with the data on the injectivity coefficient, data on changes in the mechanical drilling speed are additionally used to control the beginning and end of absorption zones.

When using ground-based (wellhead) measuring equipment, micro-changes in the injectivity coefficient during the passage of the next micro-interval are calculated using the formula:

Δc _n+1 =(Q _{out n} - Q _{out n+1} ) / (10 ^-6 ρg(h _n+1 - h _n )+(ΔP _{sn n+1} - ΔP _{sn n} )), m ³ /h⋅ MPa,

where: Q _{out n} – flow rate of flushing fluid at the well exit at the beginning of the microinterval, m ³ /h;

Q _{out n+1} - flow rate of flushing fluid at the well exit at the end of the microinterval, m ³ /h;

ρ – drilling fluid density, kg/ ^m3 ;

g – free fall acceleration, m/s ² ;

h _n+1 - well depth at the end of the microinterval, m;

h _n - well depth at the beginning of the microinterval, m;

ΔP _{сс n+1} – pressure loss of the flushing fluid in the open wellbore behind the drill pipes, acting on the bottom of the well, at the end of the microinterval, MPa;

ΔP _{сс n} - pressure loss of the flushing fluid in the open wellbore behind the drill pipes, acting on the bottom of the well, at the beginning of the microinterval, MPa.

When using underground measuring equipment in the bottom hole assembly (BHA), for example, an above-bit module or other equipment to measure the actual flow rate of the washing fluid ascending behind the drill string and the actual bottomhole pressure, at fixed bottom hole depths, microchanges in the injectivity coefficient when passing through the next microinterval are calculated according to the formula:

ΔC _n+1 = (Q _{out n} - Q _{out n+1} ) / (Р _n+1 - Р _n ), m ³ /h⋅MPa,

where: Q _{out n} is the flow rate of the flushing fluid ascending behind the drill string at the beginning of the microinterval, m ³ /h;

Q _{out n+1} is the flow rate of the flushing fluid ascending behind the drill string at the end of the microinterval, m ³ /h;

Р _n+1 – pressure at the bottom of the well at the end of the microinterval, MPa;

Р _n – pressure at the bottom of the well at the beginning of the microinterval, MPa.

Considering that the flow rates of the flushing fluid at the entrance to the well at the beginning (Q _{in n} ) and at the end (Q _{in n+1} ) of the microinterval are practically equal to each other, they are mutually excluded from the calculation formula.

Microchanges in the pickup coefficient during the passage of the next microinterval can have both positive and negative values, and each microchange in the pickup rate is counted from the value achieved one step earlier. The sum of micro-changes in the injectivity coefficient gives the absolute value of the injectivity coefficient of an open wellbore at a given depth n:

С _n =∑ Δс _n ,

where: Δс _n – microchange in the injectivity coefficient, m ³ /h⋅MPa.

The absolute values of the injectivity coefficient related to specific depths on the graph are projections of the corresponding points of the curve of changes in the injectivity coefficient onto the abscissa axis, calibrated in the dimension m ³ /h⋅MPa.

Along with the graphical representation, digital data of the injectivity coefficient are calculated.

If there is a loss of circulation of the drilling fluid in the well before it is restored, it is possible to carry out an auxiliary stage of work - periodic hydrodynamic examination of the wellbore using air defense to obtain a graph of the dependence of the flow rate of the liquid pumped into the well Q on the pressure P in order to determine the injectivity of the open hole when pumping drilling fluid and identify approximate characteristics of absorption zones. To do this, the deepening of the well is stopped at a given depth, the preventer is closed (when drilling under the casing, a wellhead release packer is used) and a study is carried out by injecting flushing fluid into the well through drill pipes, taking into account the permissible pressure. In this case, a graphical dependence of the flushing fluid flow rate on pressure is recorded at a given well depth with the simultaneous calculation of digital data for the injectivity coefficient.

Based on the dynamics of changes in the well's injectivity as it deepens, taking into account interlayer flows, the composition and properties of the flushing fluid, the well drilling mode are adjusted, and work is carried out to isolate the encountered absorption zones, taking into account the static fluid level. After reaching the design depth, the accumulated and summarized information is used for a documented forecast of the wellbore’s readiness for casing, the selection of cementing materials and well casing technology.

The proposed method for hydrodynamic diagnostics of an open hole of a well under construction will improve the scientific and technical level of drilling operations through the implementation of system principles, the basis of which are: information, organization and control of technological processes. Achieved is the prompt receipt of complete and reliable data on absorption layers and the hydrodynamic characteristics of the wellbore under construction, an adequate selection of materials and technology for drilling, isolation of absorption zones and well casing, increasing the success rate and reducing the time and money spent on carrying out these works. This technology is aimed at improving the quality, reliability and durability of the well, therefore, an increase in its operational capabilities and an increase in production are expected.

Claims (17)

A method for hydrodynamic diagnostics of an open hole of a well under construction, including determining the injectivity coefficient of its walls by injecting flushing fluid into the well while controlling the pressure and fluid flow rate in the well-rock system, characterized in that the determination and registration of the injectivity coefficient of the well walls is carried out in the process of continuous mechanical drilling , without stopping to study the well and without a packer, with obtaining graphical and digital data on the injectivity coefficient of the well walls and the dependence of the flow rate of fluid pumped into the well on pressure in real time, by dividing the wellbore into microintervals in which the flushing parameters and depth change slightly according to compared with the length of the well, and taking into account the microchange in the injectivity coefficient when passing through the next such microinterval, while the microchange in the injectivity coefficient with _n+1 when passing the next such microinterval is calculated using the formula: - when using ground-based measuring equipment: with _n+1 = (Q _{out n} - Q _{out n+1} ) / (10 ^-6 g(h _n+1 - h _n )+( P _{sns n+1} - P _{sns n} )), m ³ /h⋅MPa, where Qout _n is the flow rate of the flushing fluid at the well exit at the beginning of the microinterval, m ³ /h; Q _{out n+1} – flow rate of flushing fluid at the well exit at the end of the microinterval, m ³ /h; – drilling fluid density, kg/ ^m3 ; g – free fall acceleration, m/s ² ; h _n+1 – well depth at the end of the microinterval, m; h _n – well depth at the beginning of the microinterval, m; P _{sns n+1} – loss of pressure of the flushing fluid in the open wellbore behind the drill pipes, acting on the bottom of the well, at the end of the microinterval, MPa; P _{sns n} – pressure loss of the flushing fluid in the open wellbore behind the drill pipes, acting on the bottom of the well, at the beginning of the microinterval, MPa; - when using underground measuring equipment in the bottom hole assembly: with _n+1 = (Q _{out n} - Q _{out n+1} ) / (Р _n+1 - Р _n ), m ³ /h⋅MPa, where Qout _n is the flow rate of the flushing fluid ascending behind the drill string at the beginning of the microinterval, m ³ /h; Q _{out n+1} – flow rate of the flushing fluid ascending behind the drill string at the end of the microinterval, m ³ /h; Р _n+1 – pressure at the bottom of the well at the end of the microinterval, MPa; Р _n – pressure at the bottom of the well at the beginning of the microinterval, MPa.