Novel gas lift process design method based on hydrops dynamic change

Abstract

The invention relates to a novel gas lift process design method based on hydrops dynamic change. The problems that in the current tight gas exploitation field, the gas lift injection amount is unreasonable, and the gas lift duration is too long are solved. According to the technical scheme, the method comprises the steps that the relation between the liquid amount, the gas amount and the injection duration and the relation between the liquid amount, the gas amount and the starting pressure are judged through field working parameters, the injection working gas amount suitable for the current is obtained, gas lift is stopped when a gas well can carry liquid for production, and the total gas lift duration is obtained; according to the method, the invalidation of the gas lift process is avoided, the optimal injection duration and the total injection gas amount under the effective gas injection amount are determined, and the purposes of reducing cost and increasing efficiency can be achieved by real-time self-regulation and popularization and implementation on site editing programs.

Description

Technical Field

[0001] The present invention relates to the exploitation and system optimization of tight gas, belonging to the field of tight gas drainage production. Background Art

[0002] The oil and gas resources in tight gas fields are well-known for their "three lows", namely, low permeability, low pressure, and low abundance. In the initial development, the reservoir pressure is relatively high and the production effect is good. However, as production progresses, the reservoir pressure gradually decreases and the production volume also decreases accordingly.

[0003] During the development of tight gas fields, gas well liquid loading is a common and intractable problem, which is particularly prominent in the low-pressure stage. Due to the low-permeability characteristics of tight gas reservoirs, the gas flow velocity is slow and is not sufficient to carry the condensate water and formation water produced. These liquids will accumulate in the wellbore, increasing the bottom-hole backpressure and hindering the flow of natural gas from the reservoir into the wellbore, thereby resulting in a reduction in production volume. Severe liquid loading may cause the gas well to exhibit a "panting" phenomenon, that is, the gas well can produce normally for a period of time, but then is forced to stop due to excessive liquid accumulation until the liquid naturally drains or measures are taken to deal with it before production can resume. Moreover, long-term liquid loading may cause corrosion or other forms of damage to downhole equipment, increasing the maintenance cost and risk.

[0004] To solve the problem of gas well liquid loading, gas lift drainage, as an effective lifting method, is widely used in tight gas fields. Gas lift drainage injects high-pressure gas into the wellbore and uses the thrust formed by gas expansion to push the accumulated liquid from the bottom of the well to the ground, thereby restoring and maintaining the normal production of the gas well. However, there is still no clear guiding method on how to judge the gas lift rate and the total process duration according to the degree of gas well liquid loading. Summary of the Invention

[0005] Object of the present invention: To solve the problems such as unreasonable gas injection volume and too long gas lift duration existing in the current tight gas exploitation field, a new method for reasonably giving the gas lift rate and the total process duration according to the degree of gas well liquid loading needs to be designed.

[0006] To achieve the above object, the present invention provides a new method for designing a gas lift process based on the dynamic change of liquid accumulation, and this technology includes the following steps:

[0007] S100: For each moment, assume an injection volume Q g Inject it into the annulus between the tubing and the casing. At the nth moment of gas lift drainage and the jth section of the wellbore tubing, use the Hagedorn-Brown method to calculate the pressure at this node as p(n, j) and calculate the v sg (n, j), v s1 (n, j) and H1(n, j) values, where the liquid apparent flow velocity is defined as v s1 = q w / A, with its unit defined as m / s, q w is the daily water production, with its unit defined as m 3 / s, A is the cross-sectional area of the tubing, with its unit defined as m, and the apparent gas velocity is defined as v sg = q sc B g / A, with its unit defined as m / s, q sc is the daily gas production, with the unit defined as m 3 / s, and the expression for the volume coefficient of natural gas is B g has no unit, Z is the deviation factor, with no unit, P sc is the standard condition pressure, with the unit defined as MPa, P is the gas reservoir pressure, with the unit defined as MPa, and calculating H l requires four dimensionless parameters, namely the dimensionless gas velocity dimensionless liquid velocity dimensionless fluid viscosity dimensionless pipe diameter where ρ g is the gas density, and its expression is with the unit defined as kg / m 3 , ρ l is the liquid density, and its expression is ρ l = 1000γ w , with the unit defined as kg / m 3 .

[0008] S200: Obtain the gas lift startup pressure, whose value is determined by the formula P 启动 = P 柱塞 + P 油压 + P 摩擦 + ρ m gh, where the plunger movement pressure is determined by the material and size of the plunger itself, the oil pressure is measured at the wellhead of the gas well, and the frictional resistance along the way is obtained from the formula P 摩擦 = f m H, where the friction coefficient f m is obtained from the formula , with no unit, where the Reynolds number R em is obtained from the formula , with no unit, v m , ρ m , u m are the mixture velocity, density, and viscosity respectively, where v m is obtained from the formula v m = v sg + v sl obtained, with the unit defined as m / s, ρ m is obtained from the formula ρ m = ρ1H1 + ρg (1-H1) is obtained, and the unit is limited to kg / m 3 , u m is obtained from the formula , and the unit is limited to Pa·s. The obtaining steps of the liquid holdup are shown in S100.

[0009] S300: Obtain the liquid accumulation volume and height change in the gas well during the gas injection process. First, record the liquid accumulation volume at the moment before gas injection as V1=(P c -P t )(1 + 0.00008H)*100*A t . According to the Bernoulli equation (1 + kh t )P t +H t ρ=(1 + kh c )P c +H c ρ, the liquid column height of the tubing is deduced to be P t is the tubing head pressure, P c is the casing pressure, A t is the cross-sectional area of the tubing, A c is the cross-sectional area of the casing, k is a coefficient, and its value is 0.00008, ρ is the liquid density. Then, according to h c =H - H c and h t =H - H t , H t , H c , h t , h c , H c is the liquid column height of the casing, h t is the non-liquid column height of the tubing, h c is the non-liquid column height of the casing. At this time, the dynamic liquid level pressure of the tubing is P t1 =P t (1 + 0.00008h t ), the bottom hole tubing head pressure is P t2 =P t1 +0.01H t , the average pressure of the gas column above the tubing wellbore is P avt1 =(P t +P t1 ) / 2, the liquid accumulation volume in the tubing is V t液柱 =h t *A t , record nRT t =P avt1 *V t液柱 , the dynamic liquid level pressure of the casing is P c1 =P c (1 + 0.00008hc ), the bottom-hole casing pressure is P c2 = P c1 + 0.01H c , the average pressure of the gas column above the casing wellbore is P avc1 = (P c + P c1 ) / 2, the casing liquid holdup is V c液柱 = h c * A c , denote nRT c = P avtc * V c液柱 , at this time the bottom-hole pressure is P wf = (P t2 + P c2 ) / 2, the formation gas and liquid inflow at the next moment is Q w = Q sc * WGR, the change in liquid holdup is V l = V l + Q w / 60 / 24, nRT tg = 0.101 * Q sc * 10000 / 60 / 24 * RR, nRT cg = 0.101 * Q sc * 10000 / 60 / 24 * (1 - RR), at this time the new average static gas column pressures of the tubing and casing are P avt1 = nRT t / V t液柱 、P avc1 = nRT c / V t液柱 , at this time the new tubing and casing pressures are P t = P avt1 (1 - 0.00008 * ht / 2)、P c = P avc1 (1 - 0.00008 * h c / 2), at this time the new bottom-hole tubing and bottom-hole casing pressures are P t2 = P t1 + 0.01H t 、P c2 = P c1 + 0.01H c , the new bottom-hole pressure is P wf = (P t2 + P c2 ) / 2, substitute the new P t , P c , V l Repeat the above steps to obtain the new H t 、H c 、ht and h c , thereby obtaining H at different times t , H c , h t , h c . The above liquid volume unit is m 3 , and the gas volume unit is 10 4 / m 3 , the pressure unit is MPa, the height unit is m, the cross-sectional area unit is m 2 , and the density unit symbol is kg / m 3 .

[0010] S400: Different critical liquid-carrying models are adopted according to different well types to determine whether liquid-carrying production can be achieved. The Wang Yizhong model is adopted in vertical wells and the Tan Xiaohua model is adopted in horizontal wells where v is the critical liquid-carrying flow velocity, the unit is limited to m / s, σ is the surface tension, the unit is limited to N / m, ρ l is the liquid density, the unit is limited to kg / m 3 , ρ g is the gas density, the unit is limited to kg / m 3 , μ g is the gas viscosity, the unit is limited to Pa·s, D is the tubing diameter, the unit is limited to m, Q s1 is the daily water production, the unit is limited to m 3 / d, θ is the well deviation angle, the unit is limited to °. If liquid-carrying production can be achieved by gas lift at this time, then the gas lift is stopped to achieve the purpose of reducing costs and increasing efficiency in the process economy. This moment is the total duration of the gas lift process Description of the Drawings

[0011] In the drawings:

[0012] Figure 1 Method technical roadmap

[0013] Figure 2 Relationship diagram of liquid volume, gas volume and injection duration

[0014] Figure 3 Relationship diagram of liquid volume, gas volume and startup pressure

[0015] Figure 4 Variation diagram of the liquid accumulation height in the oil and casing during gas lift

[0016] Figure 5 Effect diagram of achieving critical liquid-carrying production after gas lift Detailed Implementation Modes

[0017] The following describes the present invention in detail according to the Figure 1 technical roadmap and preferred embodiments in it. The method includes the following steps:

[0018] Step 1: At time t0, set an injection gas volume Q g Inject it into the annulus between the tubing and the casing. At this moment, when it comes to the j-th section of the wellbore tubing, use the Hagedorn-Brown method to calculate the pressure at this node as p(n, j) and calculate the v at this point sg (0, j), v s1 (0, j) and the value of H1(0, j). The value range of j is 0 to H, where H is the wellbore depth, and the unit is limited to m. Denote the water production volume at the moment before gas injection as Q w , accumulate the liquid holdup rates in the range of 0 to H, denoted as H1(0, sum). The water production volume at the injection gas volume at this moment is Q w +H1(0, sum). At the same time, enter the next moment t1, and the water production volume at the injection gas volume obtained by repeating the above steps is Q w +H1(0, sum)+H1(1, sum), until the set last moment n. The water production volume at the injection gas volume at this moment is Q w +H1(0, sum)+H1(1, sum)+……+H1(n, sum). At the same time, set different initial wellhead pressures to obtain the relationship diagrams of liquid volume, gas volume and injection duration under different initial wellhead pressures, such as Figure 2 .

[0019] Step 2: Obtain the gas lift startup pressure at the calculation moment, and its value is determined by the formula P 启动 =P 柱塞 +P 油压 +P 摩擦 +ρ m gh. Among them, the plunger movement pressure is determined by the material and size of the plunger itself, the oil pressure is measured at the wellhead of the gas well, use the Hagedorn-Brown method to calculate the pressure at the bottom of the well as p and calculate the v at this point sg 、v sl and H l values, and then obtain the mixture density, mixture velocity, density and viscosity. Among them, v m is obtained by the formula v m =v sg +v s1 acquire, ρ m is obtained by the formula ρ m =ρ1H1+ρ g (1 - H1) acquire, u m is obtained by the formula acquire, and then obtain the Reynolds number and the friction factor Finally, obtain the frictional resistance along the path P 摩擦 =f mH. Since the startup pressure is closely related to the gas injection volume, in order to obtain a reasonable gas injection volume, different gas injection volumes are changed and substituted into the above formula to obtain the relationship diagram of liquid volume, gas volume and startup pressure as shown in Figure 3 .

[0020] Step 3: Obtain the change in the liquid accumulation volume and height in the gas well during the gas injection process. First, it is known that the liquid accumulation volume V1 at the previous moment = (P c -P t )(1 + 0.00008H) * 100 * A t and P t , P c Substitute them into to obtain the liquid accumulation height in the tubing. Then, according to h c = H - H c and h t = H - H t to obtain the liquid accumulation height H c . At this time, the flowing wellhead pressure in the tubing is P t1 = P t (1 + 0.00008h t ), the bottom hole tubing pressure is P t2 = P t1 + 0.01H t . The average pressure of the gas column above the tubing wellbore is P avt1 = (P t + P t1 ) / 2. The liquid accumulation volume in the tubing is V t液柱 = h t * A t . Denote nRT t = P avt1 * V t液柱 . The flowing wellhead pressure in the casing is P c1 = P c (1 + 0.00008h c ), the bottom hole casing pressure is P c2 = P c1 + 0.01H c . The average pressure of the gas column above the casing wellbore is P avc1 = (P c + P c1 ) / 2. The liquid accumulation volume in the casing is V c液柱 = h c * A c . Denote nRT c = P avtc * V c液柱 . At this time, the bottom hole pressure is P wf = (P t2 + P c2 ) / 2. The formation gas and liquid inflow at the next moment is Qw = Q sc * WGR, the change in liquid accumulation volume is V l = V l + Q w / 60 / 24, nRT tg = 0.101 * Q sc * 10000 / 60 / 24 * RR, nRT cg = 0.101 * Q sc * 10000 / 60 / 24 * (1 - RR), at this time the average static gas column pressure P of the new tubing and casing avt1 = nRT t / V t液柱 、P avc1 = nRT c / V t液柱 , at this time the new tubing pressure and casing pressure are P t = P avt1 (1 - 0.00008 * ht / 2)、P c = P avc1 (1 - 0.00008 * h c / 2), at this time the new bottom-hole tubing pressure and bottom-hole casing pressure are P t2 = P t1 + 0.01H t 、P c2 = P c1 + 0.01H c , the new bottom-hole pressure is P wf = (P t2 + P c2 ) / 2, repeat the above steps with the new Pt, Pc, Vl to obtain the new obtained H t 、H c 、h t 、h c , and then obtain H at different times t 、H c 、h t 、h c , plot the time and H t 、H c in the figure as shown in Figure 4 .

[0021] Step 4: During gas lift, simultaneously evaluate whether liquid-carrying production can be achieved. In vertical wells, use the Wang Yizhong model According to different well types, adopt different critical liquid-carrying models to judge whether liquid-carrying production can be achieved. In horizontal wells, use the Tan Xiaohua model If liquid-carrying self-production can be achieved through gas lift at this time, then stop gas lift to achieve the purpose of reducing costs and increasing efficiency in the process economy

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) Considering whether the gas lift is effective to avoid the invalidation of the process; (2) Considering the optimal injection duration and the total injection gas volume under the effective injection gas volume; (3) It can achieve real-time self-regulation, promote and implement the on-site editing program to achieve the purpose of cost reduction and efficiency improvement.

[0023] Finally, it should be noted that the above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the present invention can still be modified or equivalently replaced, and any modification or partial replacement without departing from the spirit and scope of the present invention shall be covered by the scope of the claims of the present invention.

Claims

1. A new method for designing a gas lift process based on dynamic changes of liquid accumulation, characterized in that: The method comprises the following steps: S100: For each moment, assume a gas injection volume Q g Injection into the casing annulus, at the nth moment of gas lift drainage, the jth section of the wellbore tubing, the pressure at the node is calculated using the Hagedorn-Brown method as p(n, j) and the v at that point is calculated sg (n, j), v sl (n, j) and H l (n, j) where the superficial velocity of the liquid is defined as v sl =q w / A, the unit is limited to m / s, q w is the daily water production, and its unit is limited to m 3 / s, A is the cross-sectional area of ​​the oil pipe, its unit is limited to m, and the gas superficial velocity is defined as v sg =q sc B g / A, the unit is limited to m / s, q sc The unit of daily gas production is limited to m 3 / s, where the expression of the volume coefficient of natural gas is B g The unit of is dimensionless, the unit of Z deviation factor is dimensionless, P sc The unit of standard pressure is limited to MPa, and the unit of P gas reservoir pressure is limited to MPa. Four dimensionless parameters are required to calculate Hl, which are dimensionless gas flow rate, Dimensionless liquid flow rate Dimensionless fluid viscosity Dimensionless pipe diameter where ρ g is the gas density, which is expressed as The unit is limited to kg / m 3 , where ρ1 is the liquid density, which is expressed as ρ1 = 1000γ w , the unit is limited to kg / m 3 ; S200: Get the gas lift start pressure, its value is given by the formula P 启动 =P 柱塞 +P 油压 +P 摩擦 +ρ m gh, where the plunger movement pressure is determined by the plunger material and size, the oil pressure is measured at the wellhead, and the friction resistance along the way is determined by the formula P 摩擦 =f m H is obtained, where f m By We get, where the Reynolds number R em By Income, v m , m 、u m are the velocity, density and viscosity of the mixture, respectively, where v m By formula v m =v sg +v sl Get, ρ m By formula m =ρ l H l +ρ g (1-H l )Get,u m By Obtain, the steps of obtaining the liquid holdup are shown in S100; S300: obtain the liquid accumulation volume and height change of the gas well during the gas injection process, first record the liquid accumulation volume before the gas injection as V1 = (P c -P t )(1+0.00008H)*100*A t According to the Bernoulli equation (1+kh t ) t +H t ρ=(1+kh c ) c +H c ρThe height of the fluid column in the tubing is According to h c =HH c and h t =HH t Get H t , H c 、h t 、h c At this time, the dynamic liquid surface pressure of the oil pipe is P t1 =P t (1+0.00008h t ), the bottom hole oil pressure is P t2 =P t1 +0.01H t , the average pressure of the gas column above the oil wellbore is P avt1 =(P t +P t1 ) / 2, the amount of fluid accumulated in the oil pipe is V t液柱 =h t *A t , remember nRT t =P avt1 *V t液柱 , casing dynamic liquid surface pressure is P c1 =P c (1+0.00008h c ), the bottom hole casing pressure is P c2 =P c1 +0.01H c , the average pressure of the gas column above the casing wellbore is P avc1 =(P c +P c1 ) / 2, the amount of fluid accumulated in the casing is V c液柱 =h c *A c , remember nRT c =P avtc *V c液柱 , at this time the bottom hole pressure is P wf =(P t2 +P c2 ) / 2, the next moment the gas and liquid volume in the formation is Q w =Q sc *WGR, the change in effusion volume is V l =V l +Q w / 60 / 24, nRT tg =0.101*Q sc *10000 / 60 / 24*RR, nRT cg =0.101*Q sc *10000 / 60 / 24*(1-RR), at this time, the average pressure of the static gas column of the new tubing and casing is P avt1 =nRT t / V t液柱 , P avc1 =nRT c / V t液柱 At this time, the new oil pressure and casing pressure are P t =P avt1 (1-0.00008*ht / 2), P c =P avc1 (1-0.00008*h c / 2), at this time, the new bottom hole oil pressure and bottom hole casing pressure are P t2 =P t1 +0.01H t , P c2 =P c1 +0.01H c , the new bottom hole pressure is P wf =(P t2 +P c2 ) / 2, the new P t , P c , V l Repeat the above steps to get a new H t , H c 、h t 、h c , and then get H at different times t , H c 、h t 、h c The above liquid volume units are m 3 , gas volume unit is 10 4 / m 3 , the pressure unit is MPa, the height unit is m; S400: Different critical liquid carrying models are used according to different well types to determine whether liquid carrying production is possible. Wang Yizhong model is used in vertical wells. Using Tan Xiaohua model in horizontal wells If gas lift can achieve self-production and liquid carrying at this time, then gas lift will be stopped to achieve the goal of cost reduction and efficiency improvement in the process economy. This moment is the total duration of the gas lift process.

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