CN105735932A - Well emptying and killing method for gas well drilling - Google Patents

Abstract

The invention discloses a well emptying and killing method for gas well drilling and particularly relates to a well emptying and killing method for gas well drilling in the field of well control for well drilling. According to the well emptying and killing method for gas well drilling, well killing can be conducted under the well emptying condition after a gas reservoir is opened during gas well drilling, and the oil gas reservoir can be effectively protected. The well emptying and killing method for gas well drilling comprises the following steps that A, the pump displacement, the mud density, the mud viscosity and the well mouth back pressure are worked out; B, the well mouth back pressure is made to reach the well mouth back pressure worked out in the step A; C, mud is prepared; D, the prepared mud is injected into a well through a drill column; E, the well mouth back pressure is controlled; F, the back pressure is regulated to zero; and G, the steps from step B to step E are executed cyclically. According to the well emptying and killing method for gas well drilling, well killing can be conducted under the well emptying condition after the gas reservoir is opened during gas well drilling, and the oil gas reservoir can be protected. The defects that in the prior art, a method for the complete process from well shaft emptying to mud circulation establishing is not available, and the accuracy and reliability are poor due to the fact that the process mostly depends on experience are overcome.

Description

Gas drilling empty well control method

Technical field

The present invention relates to a kind of gas drilling empty well control method, particularly a kind of gas drilling empty well control method being applied to drilling well control field.

Background technology

Gas drilling has the advantage that 1. rate of penetration is fast, and well construction period is short；2. can greatly reduce production expenditure, improve the yield of oil gas；3. it can be avoided that the generation of leakage；4. water-sensitive shale is overcome to cave in；5. the advantages such as reservoir can be effectively protected.Therefore, air drilling solves one of China's unconventionaloil pool effective way producing a difficult problem by being.Gas drilling needs kill-job to carry out subsequent job after opening reservoir, with conventional Well Killing condition the difference is that being gas in gas drilling pit shaft, without mud, circulation is set up as wanted kill-job need to inject mud, carry out kill-job operation, and under certain execution conditions, well is not also pushed down after returning out well head by mud, pushes down without by well afterwards.Circulate this process there is no complete method at present from empty well cylinder to setting up mud; mostly depend on experience; therefore prior art can carry out kill-job but without a kind of when empty well after gas drilling opens gas-bearing formation, it is possible to the effectively gas drilling empty well control method of reservoir protec-tion.

Summary of the invention

The technical problem to be solved is to provide and a kind of can carry out kill-job when empty well after gas drilling opens gas-bearing formation, it is possible to the effectively gas drilling empty well control method of reservoir protec-tion.

For solving the gas drilling empty well control method that the above-mentioned technical problem present invention adopts, including following step:

A, calculate pumpage, mud density, mud viscosity, wellhead back pressure according to zero flow model；

B, closing well, make wellhead back pressure reach the wellhead back pressure that step A calculates；

C, the mud density calculated according to step A, mud viscosity preparation mud；

D, turn on pump, injected into well the pumpage that the mud configured in step C calculates according to step A by drill string；

E, control wellhead back pressure, it is ensured that gas production is not returned out well head without drilling fluid before 0；

Back pressure is adjusted to 0 after returning out well head by F, liquid；

G, circulation carry out step B to F.

Further, the method regulating well head flow valve is adopted to control wellhead back pressure in described E step.

Further, the circulation time in described G step is 30 minutes.

The invention has the beneficial effects as follows: the application, based on the gas drilling empty well control method of zero liquid stream theory, can carry out kill-job when empty well after gas drilling opens gas-bearing formation, it is possible to effectively reservoir protec-tion.Compensate in prior art and circulate this process there is no complete method from empty well cylinder to setting up mud, mostly depend on the defect that experience, accuracy and reliability are not high.

Accompanying drawing explanation

Fig. 1 is Kelessidis flow pattern figure；

When Fig. 2 is the wellhead back pressure of 2MPa, gas production is with kill-job time variation diagram；

When Fig. 3 is the wellhead back pressure of 2MPa, dynamic liquid level height is with kill-job time variation diagram；

When Fig. 4 is the wellhead back pressure of 5MPa, gas production is with kill-job time variation diagram；

When Fig. 5 is the wellhead back pressure of 5MPa, dynamic liquid level height is with kill-job time variation diagram.

Detailed description of the invention

Below in conjunction with accompanying drawing, the invention will be further described.

The gas drilling empty well control method of the present invention.

For solving the gas drilling empty well control method that the above-mentioned technical problem present invention adopts, including following step:

A, calculate pumpage, mud density, mud viscosity, wellhead back pressure according to zero flow model；

B, closing well, make wellhead back pressure reach the wellhead back pressure that step A calculates；

C, the mud density calculated according to step A, mud viscosity preparation mud；

D, turn on pump, injected into well the pumpage that the mud configured in step C calculates according to step A by drill string；

E, control wellhead back pressure, it is ensured that gas production is not returned out well head without drilling fluid before 0；

Back pressure is adjusted to 0 after returning out well head by F, liquid；

G, circulation carry out step B to F.

The described parameter in engineering design calculates based on zero liquid stream model, and zero liquid stream model is:

Its assumed condition and the factor of simplification are as follows:

(1) model meets the big fundamental equation of hydrodynamics three, it may be assumed that equation of continuity, the equation of momentum, energy equation；

(2) gas-liquid slips loss 100%；

(3) this model is similar to basic multiphase flow criterion of identification, but identifies that inversion point and pressure-drop model are different.The main flow pattern of zero net flow quantity biphase gas and liquid flow flowing is approximately slug flow and stirs stream.Show as slug flow during low gas phase flow velocity, during high gas phase flow velocity, show as stirring stream.

The frictional resistance Pressure Drop of zero net flow quantity biphase gas and liquid flow is represented by:

${\mathrm{\ΔP}}_F=\frac{L_p}{L_s+L_f}(\frac{{\mathrm{\τ}}_s{\mathrm{\πDL}}_s}{A}+\frac{{\mathrm{\τ}}_f{\mathrm{\πL}}_f}{A})$

In formula:

ΔP_FFrictional resistance Pressure Drop, pa；

L_pPipe flow length, m；

τ_sYe Dan district wall shear stress, pa；

π pi；

τ_fLiquid film wall shear stress, pa.

τ_fAnd L_fTaylor Bubble Region use in conjunction momentum balance and mass balance can need to be calculated.Adopting the method similar with Taitel&Dukler, momentum balance equation and the mass balance equation that can derive Taylor Bubble Region liquid film stream are respectively as follows:

$\frac{{\mathrm{\τ}}_f\mathrm{\π}D}{H_f}+{\mathrm{\τ}}_i{S}_i(\frac{1}{H_f}+\frac{1}{1-H_f})-({\mathrm{\ρ}}_L-{\mathrm{\ρ}}_G)gA=0$

(1-h_f)(v_t-v_GF)=(1-H_s)(v_t-v_s)

τ in formula_iWith S_iThe respectively shearing stress of boundary and wetted perimeter, υ_GfFor liquid film district gas phase flow velocity.The coefficient of friction of gas-liquid interface adopts the relational expression of Wallis suggestion.Liquid film skin friction drag coefficient, Ye Dan district skin friction drag coefficient are relevant with characterisitic parameter n and K of non-Newtonian fluid, introduce non newtonian friction fluid resistance coefficient calculating formula as follows:

$\begin{array}{cc}f=\frac{16}{{\mathrm{Re}}_{MR}}& ({\mathrm{Re}}_{MR}<2000)\end{array}$

$\begin{array}{cc}\sqrt{\frac{1}{f}}=\frac{4}{n^{0.75}}log\&lsqb;{\mathrm{Re}}_{MR}{\left(f\right)}^{1-n/2}\&rsqb;-\frac{0.4}{n^{1.2}}& ({\mathrm{Re}}_{M2R}\&GreaterEqual;2000)\end{array}$

Re in formula_MRIt is the general Reynolds number of Metzner-Reed, is defined as:

${\mathrm{Re}}_{MR}=\frac{{D_H}^n{v}^{2-n}\mathrm{\&rho;}}{K}\frac{8}{{(6+2/n)}^n}$

In formula:

D_HHydraulic diameter, m；

N non-Newtonian fluid liquidity index；

V pipe flow velocity, m/s.

The total pressure drop of zero flow quantity air stripping flowing is made up of weight position Pressure Drop and frictional resistance Pressure Drop:

In formula:

Δp_tPipe flow overall presure drop, Pa；

Δp_fPipe flow frictional resistance pressure drop, Pa；

h_lLiquid holdup；

l_pTest pipe range, m；

ρ_lDensity of liquid phase, kg/m³；

ρ_gDensity of gas phase, kg/m³。

Zero flow quantity gas phase apparent velocity degree is represented by:

$v_m=\frac{Q_g}{A}=v_{sg}$

$\begin{array}{cc}{H}_L=1.5h_s(1-\frac{v_{sg}}{v_t}),& (v_{sg}<2.5m/s)\end{array}$

$\begin{array}{cc}{H}_L=h_s(1-\frac{v_{sg}}{v_t}),& (v_{sg}\&GreaterEqual;2.5m/s)\end{array}$

In formula:

v_mMixture velocity, m/s；

Q_gGas phase flow rate, m³/s；

A pipe flow area, m²；

v_sgGas phase apparent velocity, m/s；

h_sLiquid bullet liquid holdup；

v_tTalylor bubble point-to-point speed, m/s.

Wherein, liquid bullet liquid holdup can represent by Gregorg relational expression:

v_tIt is Talylor (Taylor) bubble point-to-point speed v_t, it is represented by:

v_t=c_ov_m+v_d

Drift velocity in formula:

$v_d=0.35\sqrt{gd({\mathrm{\&rho;}}_L-{\mathrm{\&rho;}}_g)/{\mathrm{\&rho;}}_L}$

The liquid holdup of slug Ye Sai district, vent plug section length and long bubble calculates:

Enlightening this research in triumphant Laixi finds: when the length of liquid slug is less than neutrality slug length, it will occurring stirring fluidised form, the minimum liquid slug length stablizing slug is 14D.For stable slug, along with the change of gas-liquid amount, the length of stable liquid slug is without significant change.

Triumphant Laixi enlightening this computing formula is proposed for annulus line:

$\frac{L_s}{D}=22.96(C\frac{v_m}{v_{rc}}+1)$

In formula:

L_sStablize slug length, m；

D annular space equivalent diameter, m；

v_rcThe bubble stable rate of climb in concentric annulus fluid, m/s, take 0.37；

v_mGas phase apparent velocity, m/s.

C takes 1.55.

The length computation in vent plug district

Slug flow to Bolus-triggered technique change time liquid plug in gas holdup with 0.52 into criterion to set up ring pipe transformation model, provide switching criterion for this as follows:

E_s=0.52

The research of gas holdup (accounting for whole slug flow unit) average in the liquid bolt of slug flow in vertical tube is obtained table below and reaches formula by Akagawa and Sakaguchi:

$E_s\frac{L_s}{L_s+L_b}=0.1$

Two formula on simultaneous it follows that

$\frac{0.1}{E_s}=\frac{L_s}{L_s+L_b}=0.193$

Minimum slug length L in slug is stablized due to mentioned above_s=14D, can try to achieve L_b=5.6D

Apply above mathematical model and can calculate zero flow quantity liquid holdup of air stripping flowing when slug flow and stirring stream, Frictional pressure drop and overall presure drop and corresponding Hydrodynamic Parameters.

2) flow pattern divides and pressure drop calculating

Research can be seen that the general relationship of multiphase flow pattern and gas phase apparent velocity in conjunction with Fig. 1 Kelessidis flow pattern figure when Liquid output is minimum.

(1) bubble stream

1. liquid holdup

Eject, without drilling fluid, the form that under condition, the bubble of motion dissipates bubble with differential at inactive liquid well head to flow up along Annular Pipe Flow complications, aggregate into air pocket once in a while.When arriving certain point when its junction frequency suddenly rises, it is changed into slug flow.According to Florence Griffith Griffith and Mo Yixisi Moissis experimentation when low fluid flow or no liquid flow, the liquid holdup critical point changed to slug flow of bubble stream is 0.7.

2. gas phase apparent velocity

The gas phase apparent velocity calculating bubble stream first to calculate single isolated bubbles movement velocity, and it is calculated as

$v_g=1.53{\&lsqb;\frac{g({\mathrm{\&rho;}}_l-{\mathrm{\&rho;}}_g)\mathrm{\&sigma;}}{{\mathrm{\&rho;}}_l^2}\&rsqb;}^{\frac{1}{4}}$

v_sg=(1-H_L)v_g

$H_L=1-\&lsqb;\frac{v_{sg}}{1.08v_{sg}+1.41{\&lsqb;\frac{g({\mathrm{\&rho;}}_l-{\mathrm{\&rho;}}_g)\mathrm{\&sigma;}}{{\mathrm{\&rho;}}_l^2}\&rsqb;}^{\frac{1}{4}}}\&rsqb;$

3. discrimination condition

$0.01\&le;v_{sg}\&le;0.4829{\&lsqb;\frac{g({\mathrm{\&rho;}}_l-{\mathrm{\&rho;}}_g)\mathrm{\&sigma;}}{{\mathrm{\&rho;}}_l^2}\&rsqb;}^{\frac{1}{4}}$

4. Pressure Drop calculates

Mixture density: ρ_m=H_Lρ_l+E_gρ_g

Reynolds number:

$A=\frac{{\left(\frac{K_a}{D_H-D_{po}}\right)}^{1.1098}}{2.8257}+{\left(\frac{7.149}{\mathrm{Re}}\right)}^{0.8981}$

The coefficient of friction resistance:

Frictional resistance gradient:

Gross pressure gradient:

${\mathrm{\&Delta;P}}_T=\frac{{\mathrm{\&rho;}}_{m}g+{\mathrm{\&Delta;P}}_f}{1-\frac{v_{sg}}{P}({\mathrm{\&rho;}}_g\&CenterDot;V_{sg})}$

(2) slug flow

1. discrimination condition

When gas phase apparent velocity 2.5m/s this time be slug flow and stir stream critical point, in conjunction with Kelessidis flow pattern figure it is also seen that about 2.5m/s be slug flow and stir stream transfer point.

$0.4829{\&lsqb;\frac{g({\mathrm{\&rho;}}_l-{\mathrm{\&rho;}}_g)\mathrm{\&sigma;}}{{\mathrm{\&rho;}}_l^2}\&rsqb;}^{\frac{1}{4}}\&le;v_{sg}<2.5$

2. Pressure Drop calculates

Introduce non newtonian friction fluid resistance coefficient calculating formula as follows:

$\begin{array}{cc}f=\frac{16}{{\mathrm{Re}}_{MR}}& ({\mathrm{Re}}_{MR}<2000)\end{array}$

$\begin{array}{cc}\sqrt{\frac{1}{f}}=\frac{4}{n^{0.75}}log\&lsqb;{\mathrm{Re}}_{MR}{\left(f\right)}^{1-n/2}\&rsqb;-\frac{0.4}{n^{12}}& ({\mathrm{Re}}_{MR}\&GreaterEqual;2000)\end{array}$

Re in formula_MRIt is the general Reynolds number of Metzner-Reed, is defined as:

${\mathrm{Re}}_{MR}=\frac{D_H{v}^{2-n}\mathrm{\&rho;}}{K}\frac{8}{{(6+2/n)}^n}$

In formula:

D_HHydraulic diameter, m；

N, k non-Newton fluid characteristic parameter.

Zero flow quantity gas phase apparent velocity degree is represented by:

$v_m=\frac{Q_g}{A}=v_{sg}$

$H_L=h_s(1-\frac{v_{sg}}{v_t})$

Wherein, liquid bullet liquid holdup can represent by Gregorg relational expression:

h_s=1/ [1+ (v_m/8.66)^1.39]

v_tIt is Talylor (Taylor) bubble point-to-point speed v_t, it is represented by:

v_t=c_ov_m+v_d

Drift velocity v in formula_d:

$v_d=0.35\sqrt{gd({\mathrm{\&rho;}}_L-{\mathrm{\&rho;}}_g)/{\mathrm{\&rho;}}_L}$

(3) stream is stirred

1. discrimination condition

$2.5\&le;V_{sg}<3.1{\&lsqb;\mathrm{\&sigma;}\&CenterDot;g\frac{({\mathrm{\&rho;}}_l-{\mathrm{\&rho;}}_g)}{{{\mathrm{\&rho;}}_g}^2}\&rsqb;}^{0.25}$

2. Pressure Drop calculates

$H_L=1.5h_s(1-\frac{v_{sg}}{v_t})$

Wherein, liquid bullet liquid holdup can represent by following relational expression:

h_s=1/ [1+ (v_m/8.66)^1.39]

v_tIt is Talylor (Taylor) bubble point-to-point speed v_t, it is represented by:

v_t=c_ov_m+v_d

Drift velocity v in formula_d:

$v_d=0.35\sqrt{gd({\mathrm{\&rho;}}_L-{\mathrm{\&rho;}}_g)/{\mathrm{\&rho;}}_L}$

(4) ring spray

1. discrimination condition

$v_{sg}\&GreaterEqual;3.1{\&lsqb;\mathrm{\&sigma;}\&CenterDot;g\frac{({\mathrm{\&rho;}}_l-{\mathrm{\&rho;}}_g)}{{{\mathrm{\&rho;}}_g}^2}\&rsqb;}^{0.25}$

2. Pressure Drop calculates

Its gas-liquid two-phase of the gas phase buoyancy-driven slippage loss ejected under condition without drilling fluid due to well head reaches 100%, therefore for itself gas holdup of ring spray under this condition close to 100%.So, under this condition, ring spray can regard the flowing calculating of pure gas column.Reynolds number:

The coefficient of friction resistance:

Frictional resistance gradient:

Gross pressure gradient: ${\mathrm{\&Delta;P}}_T=\frac{-{\mathrm{\&rho;}}_{g}g+{\mathrm{\&Delta;P}}_f}{1+\frac{v_{sg}}{P}({\mathrm{\&rho;}}_g\&CenterDot;v_{sg})}$

According to casing programme and stratum gas production, adopt different pumpage, mud density, mud viscosity, wellhead back pressure to be programmed tentative calculation, obtain suitable construction parameter, carry out kill-job according still further to suitable parameter.

Described E step adopt the method regulating well head flow valve control wellhead back pressure.Adopting the control method of adjustment well head flow valve real-time, simple to operate, governing response is fast, and accuracy is high.

Circulation time in described G step is 30 minutes.

Embodiment:

Casing programme is M-34

Assuming that initial gas production is 270,000 sides/sky, kill-job mud density is 1.0g/cm³, viscosity is 1mPa.s, and discharge capacity is 40L/min, 2MPa back pressure.

Well structure design tables of data

Three open simple drill combination

As shown in Figures 2 and 3, it is evident that carry out kill-job under the wellhead back pressure of 2MPa, when dynamic liquid level height reaches well head, gas production is also very big, is not 0, and therefore above-mentioned construction parameter is unreasonable.Now, back pressure is strengthened, if it is as follows that back pressure is added to 5MPa result:

It is 0 that dynamic liquid level height arrives gas production during well head, therefore can adopt this construction parameter.

Therefore adopt the gas drilling empty well control method step based on zero liquid stream is theoretical as follows in this well:

Step one, according to zero liquid stream model computational engineering construction parameter.

Recommending parameter is: kill-job mud density is 1.0g/cm³, viscosity is 1mPa.s, and discharge capacity is 40L/min, wellhead back pressure 5MPa

Step 2, closing well so that the back pressure of well head reaches the numerical value of engineering design；

Closing well, adjusts well head choke valve so that it is be maintained at 5MPa gradually when wellhead back pressure reaches 5MPa.

Step 3, configures the mud of corresponding density and viscosity according to the requirement of engineering design；

Configuration density is 1.0g/cm³, viscosity is the kill-job mud of 1mPa.s, actually clear water.

Step 4, turn on pump, the mud configured is injected into well by drill string according to the pumpage set；

Turn on pump, is adjusted to 40L/min by pumpage.

Step 5, regulates well head choke valve according to engineering design, controls wellhead back pressure, it is ensured that gas production is not returned out well head without drilling fluid before 0；

Step 6, back pressure is adjusted to 0 after returning out well head by liquid, circulates 30 minutes.

Wherein gas production is with the kill-job time as shown in Figure 4, and during wellhead back pressure, dynamic liquid level height changed as shown in Figure 5 with the kill-job time.

Claims (3)

1. gas drilling empty well control method, it is characterised in that: include following step:

A, calculate pumpage, mud density, mud viscosity, wellhead back pressure according to zero flow model；

B, closing well, make wellhead back pressure reach the wellhead back pressure that step A calculates；

C, the mud density calculated according to step A, mud viscosity preparation mud；

D, turn on pump, injected into well the pumpage that the mud configured in step C calculates according to step A by drill string；

E, control wellhead back pressure, it is ensured that gas production is not returned out well head without drilling fluid before 0；

Back pressure is adjusted to 0 after returning out well head by F, liquid；

G, circulation carry out step B to F.

2. right wants the gas drilling empty well control method as described in 1, it is characterised in that: adopt the method regulating well head flow valve to control wellhead back pressure in described E step.

3. right wants the gas drilling empty well control method as described in 1, it is characterised in that: the circulation time in described G step is 30 minutes.