CN103733091A - Method for determining spacing of hydraulic fractures in a rock formation - Google Patents

Abstract

Methods of the present disclosure include determining an expected trajectory of induced fractures in a rock formation, analyzing net pressure associated with the induced fractures, and determining at least one of spacing of induced fractures and a property of the induced fractures based on the net pressure. Computer-readable medium containing the method are also disclosed. Other related methods are also disclosed.

Description

For determining the method for spacing of the hydraulic fracture of rock stratum

related application

The application's case advocates according to 35U.S.C. § 119 (e) rights and interests that on June 24th, 2011, that file an application and title was No. 61/501003 U.S. Provisional Application case of " for determining the method (METHOD FOR DETERMINING SPACING OF HYDRAULIC FRACTURES IN A ROCK FORMATION) of spacing of the hydraulic fracture of rock stratum ", and the full content of described U.S. Provisional Application case is incorporated herein by reference.

Technical field

The present invention relates generally to drilling well, and more particularly, relate to a kind of method of spacing of the hydraulic fracture for definite rock stratum.

governmental approval right

The present invention carries out under the DE-AC26-07NT42677 Er government support of authorizing according to USDOE.U.S. government has certain right to the present invention.

Background technology

Can find almost there is no poriness in geological stratification hydrocarbon (for example, oil, the rock gas etc.) reservoir of (for example, shale, sandstone etc.).Described hydrocarbon can trap in the crack and pore space on stratum.In addition, described hydrocarbon can be adsorbed onto on the organic material of shale bed.The combination that develops the waterfrac treatment (" pressure break (fracing) ") that can be dependent on lateral drilling and stratum rapidly of extracting hydrocarbon from these unconventional reservoirs.Lateral drilling has allowed to carry out along the hydrocarbon reservoir of landing surface and in the hydrocarbon reservoir on stratum drilling well to catch better the hydrocarbon of trap in described reservoir.In addition, by increasing the number in the crack in stratum and/or catching more hydrocarbons via the large I that pressure break increases already present crack.The ability in the crack naturally existing in the spacing between crack and stimulation rock can be the successful key factor of the horizontal completion in unconventional hydrocarbon reservoir.

Summary of the invention

In one embodiment, disclose a kind of method, it comprises: the expection path of determining institute's created fractures; Analyze the net pressure being associated with described institute created fractures; And based on described net pressure, determine at least one in the spacing of institute's created fractures and the character of described institute created fractures.Also disclose the computer-readable media that contains described method.

In alternate embodiment, disclose a kind of method of optimizing fracture interval.Described method comprises: expansion incipient crack; Measure the pressure being associated with the described incipient crack of expansion; Determine and prevent the crossing required minimum spacing in the second crack and described incipient crack; And expand described the second crack away from least described minimum spacing distance in described incipient crack.

In other embodiments, also disclose a kind of method of optimizing fracture interval.Described method comprises: analyze the stress being associated with first group at least one crack that is associated with the first well; Analyze the stress being associated with second group at least one crack that is associated with the second well; And the spacing in definite crack being associated with Mitsui, the described crack being associated with described Mitsui is not intersected with described first group of crack and described second group of crack, described Mitsui extends between described the first well and described the second well.

In other embodiment again, also disclose a kind of method of definite maximum horizontal pressure.Described method comprises: the actual pressure during each pressure break stage of measurement rock stratum; Determine the theory expectation pressure during each pressure break stage of described rock stratum; And at least comparison based on described theory expectation pressure and described measured actual pressure and determine the maximum horizontal pressure of described rock stratum.

Accompanying drawing explanation

Fig. 1 graphic extension is according to the example schematic that is configured to extract from being rich in the shale bed of gas the gas well of rock gas of some embodiments of the present invention;

Fig. 2 a and 2b graphic extension are according to the example redirecting of the stress in the rock stratum due to crack is orthogonal to the placement of horizontal well of some embodiments of the present invention;

Fig. 3 graphic extension is according to the geometric configuration of the single transverse crack of the shale bed of some embodiments of the present invention, described shale bed comprise can comprise hydrocarbon (for example, rock gas) payzone and can be by the boundary layer of described payzone deckle circle;

Fig. 4 graphic extension is according to the three-dimensional model of a plurality of transverse cracks in the layering rock stratum of some embodiments of the present invention;

Fig. 5 graphic extension expansion as calculated that the mechanical stress based on previous crack (n) is interfered according to the follow-up crack (n+1) of some embodiments of the present invention;

Fig. 6 graphic extension is calculated the result of crack propagation according to some embodiments of the present invention about each crack of spaced apart approximately 400 feet;

Fig. 7 graphic extension is calculated the result of crack propagation according to some embodiments of the present invention about each crack of spaced apart approximately 300 feet;

Fig. 8 graphic extension is according to the stress distribution of the rock stratum of some embodiments of the present invention, and wherein said stress distribution is affected by the expansion in the crack that produces during the fourth stage of crack treatment;

Fig. 9 graphic extension according to some embodiments of the present invention about being reduced to the crack propagation of the fracture interval of 250ft;

The stress distribution of the rock stratum that Figure 10 graphic extension causes according to the crack by Fig. 9 of some embodiments of the present invention;

Figure 11 graphic extension according to some embodiments of the present invention about being reduced to the crack propagation of the fracture interval of 200ft;

Figure 12 graphic extension according to some embodiments of the present invention about being reduced to the crack propagation of the fracture interval of 150ft;

Figure 13 graphic extension is according to the impact of the fleet angle of the fracture interval fracture of some embodiments of the present invention and quadrature path;

Figure 14 graphic extension is the impact on the differentiation of clean closure stress according to the fracture interval of some embodiments of the present invention;

Figure 15 a and 15b graphic extension are according to the horizontal stress that the stress being associated with crack turns to the rock stratum in district that has of some embodiments of the present invention;

Figure 16 a and 16b graphic extension are according to the continuous pressure break of the execution of some embodiments of the present invention and replace the difference between pressure break;

Figure 17 a and 17b graphic extension are according to the stress orientation that the stress being associated with the first crack and the second crack turns to the rock stratum in district that has of some embodiments of the present invention;

Figure 18 shows the spacing that can be minimum crack according to the stress difference of some embodiments of the present invention;

In the situation of Figure 19 graphic extension optimum spacing in replacing pressure break sequence according to some embodiments of the present invention, depart from stress and can approach zero in nearly wellbore region;

Figure 20 graphic extension is according to the example of the fracture interval that can carry out about a plurality of horizontal branch wells of some embodiments of the present invention;

Figure 21 a and 21b graphic extension are according to the stress distribution between two fractures of expanding from lateral branches well of some embodiments of the present invention;

The length of " intermediate cracking " that Figure 22 graphic extension is expanded according to the different value Er Cong center Multilateral Wells for fracture length of some embodiments of the present invention is with respect to the relation between spacing between well; And

Figure 23 graphic extension according to some embodiments of the present invention can along intermediate cracking suppose that the local stress of propagation direction record is poor.

Embodiment

Fig. 1 graphic extension is configured to extract from being rich in the shale bed 102 of gas the example schematic of the gas well 100 of rock gas.Well 100 can come drilling well to be formed on 102 wells 104 that extend in shale bed 102 and along shale bed by usage level boring method.In this example, well 104 can make well 104 extend to obtain compared with the well of good yield 100 perpendicular to the maximum horizontal in-situ stress of shale bed 102 through drilling well.

Shale bed 102 can produce trap at the crack of shale bed 102 and the rock gas in pore space.Described rock gas is also in the adsorbable organic material comprising in the shale of shale bed 102.Along with well 104 extends through shale bed 102, well 104 is the extending crack through shale bed 102 (not showing clearly) also.Gas in described crack can enter well 104 and therefore can be acquired at rig 106 places of well 100.When gas leaves the crack of shale bed 102, the gas being adsorbed on organic material can be released in crack, and institute's adsorbed gas also can be acquired.The number in the crack of the shale bed 102 of passing through along with well 104 increases, and the producible gas flow of well 100 also can increase.Therefore, increase in shale bed 102 gas yield that can increase well 100 along the number in the crack of well 104.

Can use waterfrac treatment (" pressure break (fracing) ") to increase number and/or the size in 102Zhong crack, shale bed.Pressure break can refer to any technique for the crack of initial and expansion rock stratum.In addition, pressure break can be used for increasing the existing crack in rock stratum.Pressure break can comprise hydraulic fluid is pressed in the crack of rock stratum and for example, keeps opening to increase the size in crack and propping agent (, sand grains) is introduced in new created fractures so that crack.Described crack can be the existing crack in stratum, maybe can come initial by multiple technologies known in technique.Extend and expand the required amount of pressure in described crack and can be described as " frac pressure ".

As about Fig. 2 a and the further detail display of 2b, during pressure break, produce the stress characteristics that crack can change rock stratum.Therefore, from the initial follow-up transverse crack of horizontal well, can be depending on that the stress being caused by described pressure break redirects and towards or away from previous crack departing from.Stress redirects the directed function in the engineering properties, fracture interval and the previous crack that can be reservoir rock.As below described in further detail, in some instances, spacing fracture treatment is by too closely producing the follow-up crack of intersecting with previous crack.Therefore,, in these a little examples, the contribution in the follow-up crack in hydrocarbon output can be reduced or minimize.

As below further in detail disclosed, the spacing that hydrocarbon well (for example gas well 100) is carried out to fracturing operation can be measured to determine to determine with net pressure and also reduce that intersect with previous crack in follow-up crack and the minimum pressure break spacing of the possibility of interference.In some instances, net pressure can be determined by surface pressing or down-hole pressure during pressure break.Therefore, the selection of fracture interval can make to increase the number from the initial crack of horizontal hole, also reduce that crack may interfere with each other simultaneously and/or crossing possibility to allow hydrocarbon by the better productive rate of each institute's created fractures and to exhaust.Therefore, the business efficiency of pressure break can be improved and the cost that (for example, shale bed 102) obtain hydrocarbon can be reduced from tight stratum.

Can in the case of without departing from the present invention Fig. 1 be made modification, add or be omitted.For instance, although Fig. 1 is described as carrying out pressure break about shale gas stratum, the present invention can be used for improving for example, pressure break spacing for any applicable stratum (, fine and close sand grains stratum, coal-seam gas, sandstone, ls, oil shale).In addition, although well 100 is described as for extracting rock gas, should be understood that principle described herein can be used for extracting any other applicable hydrocarbon.

Fig. 2 a and 2b graphic extension are according to the example redirecting of the stress in the rock stratum due to the placement of horizontal well by crack quadrature (or laterally) of some embodiments of the present invention.Opening via the transverse crack that supports in the horizontal well of waterfrac treatment can cause redirecting around the stress in the rock stratum in crack.

Fig. 2 a can represent the stress of for example, rock stratum in horizontal plane (plane that, is parallel in fact ground).Therefore, the Z-axis of Fig. 2 a can represent in the x-direction apart from the distance at the well 204 center of level in fact.The transverse axis of Fig. 2 a can represent in the y-direction the distance at the 202 center, crack of opening apart from using fracturing technique.The Z-axis in Fig. 2 a can be followed in crack 202 in Fig. 2 a, makes the crack 202 can be in fact transverse to horizontal hole 204.In this example, crack 202 can be extended approximately 500 feet from well 204 center.Fig. 2 a graphic extension is orthogonal in fact crack around the direction of the stress on the rock stratum in the region in crack and is orthogonal to the original position direction of the maximum horizontal stress of rock stratum.Around turning to of the stress orientation in the region in crack, be attributable to put on the pressure on stratum because of pressure break.This region that stress orientation turns to can be described as stress and turns to district, as the stress by Fig. 2 turns to district 206 to show.

Described stress can be expressed as apart from the angle of the original position direction of stress with respect to the degree redirecting of the original position direction of maximum horizontal stress.Fig. 2 b graphic extension is as redirected by forming the stress with respect to maximum horizontal stress that the crack 202 of Fig. 2 a causes.For instance, at the stress of Fig. 2 a, turn in district 206, the orientation of stress can be orthogonal in fact the orientation of in-situ stress, makes stress turn to district 206 can be described as to have 90 ° of stress to redirect.Stress turns to the point of end of extent to can be described as isotropic point, and it is found in the place, approximately 140 feet, center along transverse axis apart from crack, as shown in Fig. 2 a and 2b.Distance between crack 202 and isotropic point is depicted as s in Fig. 2 b _{90 °}.

At stress, turn to outside, district, stress can be still in not parallel with the maximum horizontal stress of rock stratum orientation.For instance, in Fig. 2 a just stress turn to 206 outsides, district maximum horizontal stress direction little by little from transverse axis parallel to parallel with Z-axis.In addition, visible in Fig. 2 b, the directional angle that is adjacent to the stress in crack 204 little by little moves to 0 ° from 90 °.For instance, as shown in Fig. 2 b, in this example, along positive y direction apart from crack 202 approximately 320 feet locate and along positive x direction apart from approximately 300 feet of places of well 204, rock stratum can have the stress of 10 ° and redirect, as by s _{10 °}institute shows.Similarly, in this example, along positive x direction apart from crack 202 approximately 450 feet locate and along positive y direction apart from approximately 400 feet of places of well 204, the stress of rock stratum 200 redirects and can be 5 °, as by s _{5 °}institute shows.

The propagation direction that redirects and can affect follow-up crack of stress.For instance, the stress in the crack 202 of Fig. 2 a and 2b turns to and in district, carries out pressure break and can produce the follow-up crack (longitudinal crack) that is parallel to well 204 expansions.In these a little examples, this phenomenon (being commonly referred to stress shade) can negatively affect the efficiency in pressure break stage.As additional examples, carry out about s _{10 °}pressure break can cause follow-up crack from being orthogonal in fact approximately 10 ° of the path deviation of well 204.Therefore,, as below described in further detail, by shining upon a plurality of angles that redirect through the stress of pressure break horizontal well and horizontal stress, can estimate the path in each crack.By shining upon the path of each institute's created fractures, can determine institute's created fractures spacing, make described institute created fractures spacing to be minimized in the situation that do not lose the efficiency in each pressure break stage.

Fig. 3 graphic extension is according to the geometric configuration of the single transverse crack 302 of the shale bed 300 of some embodiments of the present invention, described shale bed comprise can comprise hydrocarbon (for example, rock gas) payzone 304 and can be by boundary layer 306a and the 306b of payzone 304 deckles circle.Crack 300 can be based on can mathematical form expressing multiple character and modeling.Described modeling can be carried out by being configured to various computer programs, model or its combination of simulation and design fracturing operation.Described program and model can comprise the instruction being stored on computer-readable media, described instruction can operate with when carrying out, carry out described step below in one or more.Described computer-readable media can comprise any system, equipment or the device that is configured to storage and search program or instruction, for example hard disk drive, CD, flash memory or any other applicable device.Described program and model can be configured to bootstrap processor or other applicable unit retrieval and carry out the instruction from computer-readable media.Below name can be used for fracture 302 and carries out modeling to describe the various character in crack 302:

E _pthe Young modulus of=payzone, Pa (psi)

E _bthe Young modulus in=boundary layer, Pa (psi)

ν _ppoisson ratio in=payzone

ν _bpoisson ratio in=boundary layer

K=dry bulk modulus, Pa (psi)

G=modulus of shearing, Pa (psi)

L _f=fracture half-length, m (ft)

H _f=crack half is high, m (ft)

H _p=payzone half is thick, m (ft)

W ₀=maximum crack width, m (ft)

σ _v=vertical in-situ stress, Pa (psi)

σ _hmax=maximum horizontal in-situ stress, Pa (psi)

σ _hmin=minimum level in-situ stress, Pa (psi)

Boundary layer 306a and 306b can have the engineering properties (E that is different from payzone 304 _p, ν _p) engineering properties (E _b, ν _b).In this example, modeling can be carried out with numerical model in crack 302, and can have the 2L of equaling along the direction of x axle _flength, can there is in the z-direction the 2h of equaling _fheight and also can there is in the y-direction the width of not showing.

The mechanical behavior of the continuous three-dimensional medium of shale bed 300 can be described as definition Eq. (2) and the Constitutive Equation Eq. (3) of equilibrium equation Eq. (1), strain with mathematical form.Can use clearly limited values of disparity scheme in each Nodes answer for 15 equational algebra systems of 15 unknown numbers (6 components of stress σ and strain stress add 3 components of velocity vector v).Einstein's summation convention can be applicable to index i, j and the k of the value of taking 1,2,3:

${\mathrm{\σ}}_{\mathrm{ij},j}=\mathrm{\ρ}\frac{{\mathrm{dv}}_i}{\mathrm{dt}}---\left(1\right)$

$\frac{{\mathrm{d\ϵ}}_{\mathrm{ij}}}{\mathrm{dt}}=\frac{v_{i,j}+v_{j,i}}{2}---\left(2\right)$

Payzone 304 can be homogeneous, isotropic and purely elastic.Hooke's law relates to the component (Constitutive Equation) of strain and stress tensor:

${\mathrm{\σ}}_{\mathrm{ij}}=2G{\mathrm{\ϵ}}_{\mathrm{ij}}+(K-\frac{2}{3}G){\mathrm{\ϵ}}_{\mathrm{kk}}{\mathrm{\δ}}_{\mathrm{ij}}---\left(3\right)$

Wherein, $K=\frac{3}{2(1-2v)}$ And $G=\frac{E}{2(1+v)}$

Due to the utmost point low-permeability of shale and the small amount of fluid leak-off during pressure break, therefore can ignore in this example the impact that poroelasticity effect redirects the transverse crack producing stress around.Yet, in other model of other rock stratum, can determine and comprise poroelasticity effect.

Modeling also can be carried out with multiple boundary condition in 300Ji crack, shale bed 302.Can allow along crack the displacement of 302 face, wherein equal net pressure p _netconstant stress add minimum in situ horizontal stress σ _hminforced on the face in crack 302 to form crack 302, or in this example, to simulate and the formation in modeling crack 302.Therefore, the size in crack 302 (for example, width, length, highly) can be partly p _netfunction.

In the end of fracturing process, crack 302 can be crowded around downwards and be made crack 302 keep the propping agent (for example, sand grains) opening.Through support the width in the crack open can be depending on through pressure break length and during fracturing process the amount of the propping agent of institute's pumping.Putting on homogeneous state of stress boundary condition on fracture plane approximates propping agent and maintains breadth extreme w ₀the required pressure of opening.This force value can be less than the required pressure of hydraulic fracture in the identical rock of expansion.For simulating enough large reservoir volume and avoiding boundary effect, border, far field can be placed in and apart from crack, equal at least three times of fracture half-length L _fdistance.Constant stress boundary condition perpendicular to " piece " face puts on outside, border.Before the opening of crack by in-situ stress initialization:

$\left\{\begin{array}{c}{\mathrm{\σ}}_{\mathrm{xx}}=-{\mathrm{\σ}}_{h\max }\\ {\mathrm{\σ}}_{\mathrm{yy}}=-{\mathrm{\σ}}_{h\min }\\ {\mathrm{\σ}}_{\mathrm{zz}}=-{\mathrm{\σ}}_V\end{array}\right.---\left(4\right)$

After the modeling in the first crack, also can carry out modeling to follow-up crack.After forming the first crack, it is (for example, not the allowing further displacement) of fixing that its geometric configuration can be expressed as.In this example, can suppose, being compressed in while opening follow-up crack of propping agent that is positioned over inner side, previous crack is insignificant.Follow-up transverse crack can be carried out modeling with being similar to the boundary condition in the first crack as described above.The three-dimensional model of for example, a plurality of transverse cracks in Fig. 4 graphic extension layering rock stratum (, the shale bed 300 with payzone 304 and frontier zone 306 of Fig. 3).

Realizing the required net pressure of contraction width can increase with each extra crack.Iterative process able to programme is to determine corresponding to given maximum crack width w for each crack ₀net pressure.Below further describe the differentiation of clean closure stress in the order pressure break of horizontal well.

Conventional fracture modeling method can be carried out modeling to being orthogonal to the crack of horizontal well completely.Yet for quantizing better the differentiation of the propagation direction in continuous transverse crack, the stress because being caused by previous crack is redirected to the follow-up crack of departing from from quadrature path, and to carry out modeling favourable.

For head it off, can make model simplification.Contrary with complete orthogonal fracture, a plurality of dipping fractures are challenging to the model on single Numerical Grid.In limited differential pattern, can be from starting to set the geometric configuration of all slits, this is difficulty extremely, and this is because the expanded-angle of follow-up transverse crack can be depending on the mechanical stress disturbance being produced by previous crack.This can need complicated and grid reconstruction consuming time after stage in each single crack.

Therefore, for compared with the object of short-cut method, in this example, clean closure stress and propagation direction can based on only previously the mechanical stress in crack interfere and calculate.The expansion as calculated that the mechanical stress of the follow-up crack of Fig. 5 graphic extension (n+1) based on previous crack (n) interfered.For example, for each follow-up crack (, crack (n+1)), at the stress along the direction perpendicular to it that a certain distance calculating for example, is formed by previous institute supporting crack (, crack (n)) apart from crack.The clean closure stress that clean closure stress in follow-up crack equals single transverse crack (in the situation that not having stress shade) adds the stress being produced by previous crack, as shown by following Eq. (5):

$p_{\mathrm{net}}^{n+1}={\mathrm{<figure-callout\; id="1"\; label="p\; net"\; filenames="HDA0000462703960000041.png,HDA0000462703960000052.png"\; state="\{\{state\}\}">p</figure-callout>}}_{\mathrm{net}}^{}+\mathrm{\&Delta;}{\mathrm{\&sigma;}}_{\mathrm{yy}}^n\left(s_f\right)---\left(5\right)$

Based on transverse crack stress distribution around, the path in follow-up crack can be by supposing that it will follow the direction of maximum horizontal stress and guestimate.This can be by determining the direction of the maximum horizontal stress of locating on one point and crack being carried out along described Directional Extension.Then, can calculate at another point of the path of the expansion along from previous point the direction of maximum horizontal stress and by that analogy with the path in the follow-up crack of guestimate, as the crack for Fig. 5 (n+1) shows.

Visible through determining average departure angle in the crack of Fig. 5 (n).Can be according to the coordinate of the final position of crack (n+1) and calculate described average departure angle (for example, θ for crack (n+1) _f(s _f)).It can be used for, and fracture (n+1) carries out modeling so that net pressure and the path of calculated for subsequent crack (n+2).

As mentioned above, the propagation direction in follow-up crack can be follow-up crack with respect to the function of the position in the region that experiences the rock stratum being redirected by the stress that causes of the previous crack of expansion.Therefore, the spacing between previous crack and follow-up crack can affect the propagation direction in follow-up crack.Below further described Fig. 6,7,9,11 and 12 graphic extensions are according to the example of the path in the described crack of the various distance between a plurality of cracks.Crack in Fig. 6,7,9,11 and 12 can be used above and determined and can be undertaken by any applicable computer program about the described process of Fig. 3 to 5.In Fig. 6,7,9,11 and 12, the crack of describing can be induced in successive stages separately.For instance, first Fig. 6,7,9,11 and 12 crack 1 can be brings out, crack 2 can be second bring out etc.As below further described, the result of simulating about the difference of the different spacing distance between crack can be used for being identified for the optimum fracture interval on certain well and/or stratum.The parameter of the rock stratum of using in the example of following table 1 graphic extension Fig. 6 to 23, as the shale gas well the Barnett from Texas (Texas) (Barnett) shale obtains.

The reservoir parameter of table 1 – Barnett shale gas well

The result of crack propagation is calculated in Fig. 6 graphic extension about each crack of spaced apart approximately 400 feet.For 400ft spacing, transverse crack can be expected away from previously crack propagation for to have little fleet angle (being less than 2 °) with quadrature path (use identical parameters and simulate) as redirected the angle of quantitative change curve according to stress demonstrated in Figure 1.When spacing is reduced to 300ft when (as demonstrated in Figure 7), be increased to and slightly surpass 5 ° (for example,, after the stage 4, average departure angle is towards value θ with the average departure angle of quadrature path _fconcentrate for=5.7 °).Carefully watch after crack path is illustrated in crack 5, crack can be at first towards previous crack propagation and then apart from a certain distance of well, crack can start away from previous crack propagation.Mark and draw diagonal crack stress distribution around and demonstrate the explaination that this is mainly inclined to behind, as demonstrated in Figure 8.

The stress distribution of Fig. 8 graphic extension rock stratum 800, wherein said stress distribution is affected by the expansion in the crack 4 of Fig. 7.According to the stress being caused by crack 4, redistribute, may draw that stress turns to area 804, wherein follow-up crack is (for example, the crack 5 of Fig. 7) can be subject to area that previous crack attracts (for example, attract area 806) and wherein follow-up crack can for example, away from another area (, repelling area 808) of previously crack propagation.In some cases, follow-up transverse crack can be expanded in as two areas being shown by crack 5.Attract the size in area 806 to can be net pressure, in-situ stress is poor and with the function at the average departure angle of the quadrature path in crack 4.In this example, for the fracture interval lower than 400ft, the starting point in crack 5 can be positioned at the attraction area 806 that the expansion by crack 4 causes, so crack 5 can back towards crack, 4 expansions attract area 806 until it leaves at first.

Fig. 9 graphic extension according to this example about being reduced to the crack propagation of the fracture interval of 250ft.Due to nearlyer spacing, fracture deviation amount can be larger.For instance, crack 2,5 and 8 can angle θ _f>5 ° away from previous crack propagation.But the most outstanding is the following fact: under the critical value of fracture interval, the attraction area being associated with crack 2,5 and 8 can cause respectively crack 3,6 and 9 to be intersected with crack 2,5 and 8 respectively.These a little crossing practice results can be the very not excretion efficiently of reservoir, even if crack is initial compared with being close to each other.

In addition, it may be noted that as calculating the path of crack 4,7 and 10, can simulate the stress distribution that two Fracture Systems carry out computing formation.For instance, because crack 3 can be intersected with crack 2, the stress distribution that therefore can affect crack 4 can be based on crack 2 and 3 both and modelings.In Figure 10, show about the stress distribution around the Fracture System of crack 2 and 3.

Figure 11 and 12 crack propagation that also graphic extension is calculated as the difference 200ft for this real case simulation and 150ft spacing.In those examples, " unsuccessful " crack (for example, the crack 3,5,7 of Figure 11 and 10 and the crack 2,4,6,8 and 10 of Figure 12) can not only intersect with previous crack, and can Longitudinal Extension to horizontal well, make via the hydrocarbon output of bringing out these cracks and can not realize increase.For these little fracture interval values, unsuccessful crack can for example, be turned to initial crack in district and be caused by the stress of the inner side, attraction area (, the attraction area 806 of Fig. 8) being associated with previous crack being positioned at of previous crack.In this example (150ft spacing), only every a pressure break stage, effectively stimulate shale, therefore may make the pith of reservoir exhaust deficiently.

The impact of the fleet angle of Figure 13 graphic extension fracture interval fracture and quadrature path.Below the critical value of fracture interval, about the large variation of the fleet angle of the spacing of spaced apart 250 feet, 200 feet and 150 feet, can negatively affect the efficiency in (as demonstrated) pressure break stage.Therefore extra cost that, the gain of the reservoir under these spacing excretion represents with crack stage number by increasing is compared and be can be limit.This result shows: because mechanical stress is interfered, therefore constantly close spacing transverse crack may not be desirable completion strategy each other.

The impact of Figure 14 graphic extension fracture interval on the differentiation of clean closure stress.As demonstrated in Figure 14, for the fracture interval of 400ft and 300ft, clean closure stress only increases with each new stage until reach stable.Yet for the fracture interval of 250 feet, 200 feet and 150 feet, net pressure can have the trend of dipping and heaving.

Calculate number of times that fine pressure split pressure is reduced to another stage from a stage and can indicate the number in the unsuccessful crack stage of identifying Figure 10,12 and 13.The reducing of crack closure stress (from a stage to another stage) can be expand to reservoir stimulate district but not by previous crack, produced while being orthogonal to well compared with gadget stress, interfere the result of (stress shade).

Therefore, as an example, in the situation of minimum spacing, when set evaluation is 150ft, effectively spacing can only equal 300ft, and this is because can be longitudinally with respect to well every a crack.Therefore, compare with 300ft spacing, for 150ft spacing, stage number doubles to grant the minimum improvement of well production rate.

Therefore,, as shown, departing from of the quadrature path with crack carried out to the new dipping and heaving trend in differentiation that modeling can demonstrate clean closure stress above.This dipping and heaving trend can indicate the spacing between crack to be too near to and any improvement that can not produce well production rate.Therefore, can analyze clean closure stress under various spacing to determine the nearest spacing that may not produce dipping and heaving net pressure, make to determine the optimum spacing in crack.In addition, be to determine suitably clean closure stress, can estimate the propagation direction in each crack, but not as the hypothesis propagation direction carrying out be traditionally orthogonal to well.

Fracture interval also can be by analyzing that the stress that be associated with previous crack turns to district and by turn to initial follow-up crack outside district to determine at stress.For instance, Figure 15 a and 15b graphic extension have the horizontal stress that the stress being associated with crack (n+1) turns to the rock stratum 1500 in district 1502.Can extend along the Z-axis of Figure 15 a and 15b in crack (n+1) and well 1504 can extend along transverse axis.As shown in Figure 15 a and 15b, stress turns to district 1,502 1502 to extend about 230ft along well 1504 from crack, as by isotropic point s _{90 °}institute shows.Therefore, apart from crack (n+1) nearby can not initial follow-up crack than 230ft (for example, crack (n+2)), this is that follow-up crack can be expanded abreast and can not increase the hydrocarbon output from well 1504 with well 1504 because as mentioned above.

In addition, Figure 15 b graphic extension in this example, at a s _{10 °}(for example, (n+1) about 430ft apart from crack) located, and the stress of rock stratum 1500 redirects and can be 10 °, and at a s _{5 °}(for example, (n+1) 600ft apart from crack) located, and the stress of rock stratum 1500 redirects and can be 5 °.The stress of 10 ° and 5 ° redirects and can make at a s _{10 °}with s _{5 °}between initial follow-up crack (for example, crack (n+2)) can not intersect with crack (n+1), although follow-up crack can stress redirect and how much depart from from quadrature path.

When above-mentioned example is illustrated in continuous initial crack, analyze stress and turn to the large I in district how for determining the spacing in crack, yet the spacing that replaces initial crack also can turn to district to determine by analyzing the stress being associated with crack.Figure 16 a and 16b graphic extension are carried out continuous pressure break and are replaced the difference between pressure break.In Figure 16 a, visible, order is initial one by one continuously in each crack starting with crack " 1 ".Yet, in Figure 16 b, visible, initial two cracks (for example continuously, the crack of Figure 16 b " 1 " and " 2 "), yet, two previous cracks can be sufficiently far spaced apart so that the 3rd crack (for example, the crack of Figure 16 b " 3 ") can be initial between two previous cracks, make crack alternately.

Figure 17 a and 17b graphic extension have the stress orientation that the stress being associated with crack " 1 " and crack " 2 " respectively turns to the rock stratum 1700 of district 1701 and 1702.In this example, crack " 1 " and " 2 " can be through placing distance about 650ft each other.Figure 17 b graphic extension in this example stress turns to the distance between district 1701 and 1702 to can be about 20ft.Therefore, by the initial crack, centre " 3 " of " 1 " and " 2 " in crack, can by the narrow limit of 20ft avoid stress turn to district 1701 and 1702 both.In some instances, this little limit can be considered to too little and therefore may increase the spacing between crack " 1 " and " 2 ".The spacing of Figure 17 a and 17b graphic extension crack " 1 " and " 2 " can make stress turn to the district 1701 and 1702 can be non-intersect through determining, but also makes it spaced apart with permission initial the 3rd crack between it sufficiently far.Therefore, for example, by alternately (analyzing two " end " cracks in pressure break, crack " 1 " and " 2 ") stress turn to the size in district, can for example, for the placement of " centre " crack (, crack " 3 ") and spacing is between the two determined on more efficient ground.

In addition, by analyzing the amount of stress varied curve by the rock stratum 1700 due to crack " 1 " and " 2 ", visible, the stress being caused by crack " 1 " and " 2 " redirects and can cancel each other out in fact, makes the crack " 3 " can be along " 1 " and " 2 " equidistant quadrature path in fact expansion apart from crack.Therefore, can be by analyzing that stress turns to district and further graphic extension and support the alternately advantage of pressure break.

The impact of crack sequence also can affect crack complicacy.Hydraulic fracture can be and is called relative net pressure R with the interaction of already present dry _nthe function of term.This parameter can depart from stress with the part of wherein crack propagation and be inversely proportional to, as shown in following equation (6).

$R_n=\frac{p_f-{\mathrm{\&sigma;}}_{h\min }}{{\mathrm{\&sigma;}}_{h\max }-{\mathrm{\&sigma;}}_{h\min }}---\left(6\right)$

Relative net pressure R _nhigh value can contribute to path, crack complicacy.Therefore, hydraulic fracture is expanded the larger net that can form interconnection crack in low stress Cha district.The local stress that the crack of expanding by calculating experiences is poor, and alternately the habit of pressure break sequence generation crack complicacy can be quantized and can compare with more conventional fracturing process.Alternately the mean value of the visible stress difference in intermediate cracking of passing through expansion in pressure break sequence can be for crack, outside (2s _f) between spacing different value and measure.In this example, Figure 18 shows that the spacing that stress difference is minimum can equal the minimum crack spacing (325ft) previously calculating.Therefore the minimum crack spacing, replacing in pressure break sequence also can be the optimum situation that forms crack complicacy.

In the sequence of crack, along its propagation direction, by the poor alternately pressure break of relatively using of the visible local stress in crack, continuous pressure break is being proved to the improvement that produces crack complicacy continuously and alternately.Figure 19 is illustrated in and in the situation of the optimum spacing in pressure break sequence (325ft) alternately, departs from stress can approach zero in nearly wellbore region.In this example, along the first half expansions, stress difference can keep below 10psi, its can equal in-situ stress poor 10%.The only poor remarkable increase of local stress in the second half crack propagations.Therefore,, as the result of the expansion of " intermediate cracking ", select alternately pressure break sequence can produce high crack complicacy in nearly wellbore region.

The analysis of the stress that rock stratum experiences also can be used for determining the fracture interval about a plurality of horizontal branch wells.The example of the fracture interval that Figure 20 graphic extension can be carried out about a plurality of horizontal branch wells.Figure 20 graphic extension can be extended in fact in parallel with each other through three horizontal well (HW of the hydrocarbon reservoir in can horizontal plane parallel to the ground in fact ₁, HW ₂and HW ₃).

The well of Figure 20 can be by representing flaw size (L _f, h _f), fracture interval (s _f) and well between spacing (s _w) variable describe.In this example, intermediate wells (HW ₂) be for example used in, from previous two initial fractures (, the well HW of outside well ₁crack " 1 " and " 2 " and well HW ₃crack " 1 ' " and " 2 ' ") between vee crack (for example, crack " 3 ").In thering is an inhomogeneous number Multilateral Wells any horizontal completion of (and certainly, surpassing an only Multilateral Wells), can adopt same policy.This strategy can allow to benefit from the expansion of " intermediate cracking ", as in replacing pressure break completion, in the situation that not needing special subsurface tool.In fact, for example, at each Multilateral Wells (, HW ₁, HW ₂and HW ₃) in, can the initial crack of conventional continuous sequence.

Spacing between crack in these a little multiple-limb sequences can for example, be determined by analyzing the stress distribution (, stress turns to district) being associated with crack.For instance, in Figure 21 a and 21b, show from lateral branches well HW ₁and HW ₃two fractures (for example, the well HW of Figure 20 of expansion ₁crack " 1 " and " 2 " and well HW ₃crack " 1 ' " and " 2 ' ") between stress distribution.In this example, for reservoir quality and the fracture geometry of table 1, can be based on by well HW ₁crack " 1 " and " 2 " and crack " 1 ' " and " 2 ' " stress that causes directed and distribute and determine the fracture interval s being associated with the crack of each well _f(for example, well HW ₁crack " 1 ", " 2 ", " 4 ", " 6 ", " 8 " etc., well HW ₂crack " 3 ", " 5 ", " 7 ", " 9 " etc. and well HW ₃crack " 1 ' ", " 2 ' ", " 4 ' ", " 6 ' ", " 8 ' " etc. between spacing) can equal 600ft and well HW ₁, HW ₂with HW ₃between well spacing (s _w) can approximate 500ft.

Above-mentioned spacing can be determined by analyzing the direction of the maximum horizontal stress being associated with crack.For instance, the direction of maximum horizontal stress can be along the turning to of lateral branches well, as shown in Figure 21 a and 21b Anywhere.Therefore, too near-earth is spaced apart and can not be similar to alternately pressure break sequence and allow transverse crack from lateral branches well HW crack, outside " 1 " and " 2 " ₁and HW ₃expansion.

When considering again pressure break center branch well, the direction of maximum horizontal stress can still allow the expansion of transverse crack.For instance, HW ₂the distance L extending transversely in crack " 3 " _transversecan apart from previous crack intermediate distance everywhere in maximal value, and can be not only the function of the spacing between crack, outside but also be spacing (s between well _w) function.When marking and drawing the angle that stress redirects, also can identify the area of transverse crack expansion, as shown in Figure 21 b.

Figure 22 graphic extension for example, for " intermediate cracking " (, HW of the different value Er Cong center Multilateral Wells expansion of fracture length ₂there is length L _transversecrack " 3 ") length with respect to the relation between spacing between well.Visible, if described well is too far towards one anotherly spaced apart, can there is not (for example, s in the chance of expanding horizontal intermediate cracking from center Multilateral Wells so at all _w/ L _f=0.1), this is promptly to intersect because crack Ke Yu circle connects other Multilateral Wells utmost point of center branch well.For instance, if HW ₁and HW ₃length with respect to the crack in Figure 20 " 3 " is fully close to HW ₂, crack " 3 " can promptly intersect with at least one another cracks and/or well so.Therefore, the length of transverse crack expansion can increase and can between well, spacing at least equal fracture length (for example, s with spacing between well _w/ L _f=2) time, reach its maximal value.

L _transversealso can be with crack, outside (s _f) between spacing and increase.If fracture interval at least equals to replace the twice (2s of the minimum crack spacing in pressure break sequence _f=650ft), transverse crack expansion can be unaffected so.In this case, stress redirects angle along can equal zero Anywhere apart from the equidistant line in crack, outside.

Figure 23 graphic extension can be along intermediate cracking (for example, the crack of Figure 20 " 3 ") suppose that the local stress of propagation direction record is poor.This quantity is for spacing (s between minimum possibility well _w/ L _f=1) can be minimum value and also can be responsive to gap ratio fracture spacing between well.Therefore, being close to each other (but unlike equaling the high near distance in crack half) comes position level Multilateral Wells favourable.Otherwise, can lose the benefit of transversely crack propagation.In fact, this can produce the pressure break area of the reservoir having stimulated.

Return and check Figure 21 a, when between well, hour, the distance of transverse crack expansion is can fracture spacing responsive for spacing.When fracture interval is reduced to 600ft (this is only the difference of 50ft spacing) from 650ft, length extending transversely can reduce to surpass 50%.Therefore, in this example and be similar to the situation of the alternately pressure break sequence in single well, the spacing between crack, outside can at least equal 650ft.

Finally, the optimum multilateral well completion strategy of the typical Barnett shale gas well in this example can be summarized as follows:

$\left\{\begin{array}{c}{s}_w=L_f=500\mathrm{ft}\\ s_f=650\mathrm{ft}\end{array}\right.$

Institute's predicted value of transverse crack expansion and the mean stress of intermediate cracking is poor is:

$\left\{\begin{array}{c}{L}_{\mathrm{transverse}}=L_f=500\mathrm{ft}\\ \mathrm{\&Delta;}{\mathrm{\&sigma;}}_{\mathrm{hmiddlefrac}}=0.24\mathrm{\&Delta;}{\mathrm{\&sigma;}}_{\mathrm{hi}}=24\mathrm{psi}\end{array}\right.$

For example, although finally it may be noted that 650ft spacing replaces in pressure break sequence (, can be only at pressure break interval again for 20ft is when wide) at some and can be unpractically, this spacing can be enough in multilateral well completion.In situation after a while, intermediate cracking can be initial from intermediate wells (but not from outside well), and pressure break interval is enough wide bunch initial from multi-openings with crack allowance again herein.

Therefore, by the stress of analyzing by the rock stratum due to fracturing operation, redirect district, can determine that the spacing in crack, to improve from well yield, also improves the efficiency of each fracturing operation simultaneously.This stress redirect analyze can be used for continuous pressure break, for pressure break alternately and/or for a plurality of horizontal fracturing operations.

In addition, in-situ stress poor (its between maximum horizontal stress and minimum level stress poor) can affect the stress interference being formed by a plurality of continuous cracks (comprising crack intersects).Therefore, the differentiation of the frac pressure during the multistage of horizontal well pressure break can be subject to that in-situ stress is poor to be affected, for example, just as it is subject to fracture interval (, as demonstrated in Figure 14) impact the same.

Although can be easy to obtain minimum level stress from mini frac test, maximum horizontal stress can be difficult to assessment at the scene.Know the value of maximum horizontal stress provable in a plurality of problems of engineering designs in oil and gas industry (comprising waterfrac treatment and hole stability and sand grains production problems) carry out modeling, be useful.

Institute's suggesting method can be used for the differentiation of calculating the clean closure stress in given well for the different value of maximum horizontal stress.By institute's calculating pressure quantitative change curve and on-the-spot measured frac pressure are compared, can determine in question well the value of maximum horizontal stress.

Can in the situation that not deviate from scope of the present invention, above each figure be made modification, add and be omitted.For instance, only for illustration purposes, with respect to specific rock property and Size of Crack, above-mentioned model and each figure are described.Principle as described above can be used for any other applicable rock stratum.

In addition, also understand, the stress redistribution of the rock stratum being caused by vee crack also can be the function of the institute's created fractures length, fracture width, fluid rheology and the injection rate that are associated with vee crack.As mentioned above, the expansion in the follow-up crack function of the stress redistribution that previous crack causes of can serving as reasons.Therefore, analysis as described above also can be used for determining one or more to improve preferably pressure break efficiency in mentioned character above.For instance, in some examples of specific Size of Crack, determine that optimum spacing can be spaced apart too far away.Therefore, can be fixed value by spacing setting and can revise and can affect another factor that stress redirects (for example, fracture width).Can be for the different value of fracture width and calculated stress redirects and expansion and the clean closure stress in crack continuously, make to determine the optimal width in crack.

Claims (21)

1. a method, it comprises:

Determine the expection path of institute's created fractures;

Analyze the net pressure being associated with described institute created fractures; And

Based on described net pressure, determine at least one in the spacing of institute's created fractures and the character of described institute created fractures.

2. method according to claim 1, wherein determine that the expection path of institute's created fractures comprises:

The stress before pressure break is brought out in analysis;

The path in the first crack is carried out to modeling;

Modeling path based on described the first crack and determine the impact on described stress; And

Based on what caused by described the first crack, the impact of described stress is carried out to modeling to the path in follow-up crack.

3. method according to claim 2, it further comprises at least based on described first and the modeling in follow-up crack and reduce the spacing of institute's created fractures.

4. method according to claim 1, it further comprises definite maximum horizontal stress.

5. method according to claim 1, the character of wherein said institute created fractures comprises the expection path of institute's created fractures subsequently.

6. method according to claim 1, wherein determines described net pressure by the surface pressing during pressure break or at least one in down-hole pressure.

7. a method of optimizing fracture interval, it comprises:

Expansion incipient crack;

Measure the pressure being associated with the described incipient crack of expansion;

Determine and prevent the crossing required minimum spacing in the second crack and described incipient crack; And

Away from least described minimum spacing distance in described incipient crack, expand described the second crack.

8. the method for optimization fracture interval according to claim 7, it further comprises:

Measure the pressure being associated with described the second crack of expansion;

Determine and prevent crossing the second required minimum spacing in the 3rd crack and described the second crack; And

Away from being stitched to less described the second minimum spacing distance, described secondary fissure expands described the 3rd crack.

9. the method for optimization fracture interval according to claim 8, wherein determines that described the second minimum spacing is the pressure based on being associated with described the second crack of expansion at least.

10. the method for optimization fracture interval according to claim 7, wherein expands described the second crack being enough to allow to expand trilete distance between described the first crack and described the second crack.

The method of 11. optimization fracture intervals according to claim 10, it further comprises:

The pressure based on being associated with expansion described the first crack and described the second crack and determine and prevent the crossing required spacing in described the 3rd crack and described first and second crack at least; And

At least based on preventing that described the 3rd crack and described first and second crack from intersecting required spacing and the pressure that is associated with described the second crack of expansion and determine the distance reducing between the 4th crack and described the second crack.

The method of 12. optimization fracture intervals according to claim 7, wherein determine that described minimum spacing comprises:

At least based on the expansion pressure that is associated of described the first crack, the stress being caused by described the first crack being carried out to modeling; And

Based on described modeling stress, the path in described the second crack is carried out to modeling.

The method of 13. optimization fracture intervals according to claim 7, wherein determine described minimum spacing comprise at least based on net pressure, in-situ stress is poor or with the average departure angle of the path in described the first crack to the attraction area being associated with described the first crack and repel at least one in area and carry out modeling.

The method of 14. optimization fracture intervals according to claim 13, the outside, attraction area that wherein said minimum spacing is being associated with described the first crack.

The method of 15. optimization fracture intervals according to claim 13, wherein determines that described minimum spacing further comprises that counter stress turns to district to carry out modeling.

16. 1 kinds of methods of optimizing fracture interval, it comprises:

Analyze the stress being associated with first group at least one crack that is associated with the first well;

Analyze the stress being associated with second group at least one crack that is associated with the second well; And

Determine the spacing in the crack be associated with Mitsui, make the crack that is associated with described Mitsui not with described first group and described second group of crack crossing, described Mitsui extends between described the first well and the second well.

The method of 17. optimization fracture intervals according to claim 16, wherein determine that the spacing in the crack being associated with described Mitsui comprises:

The stress being associated with described first group and described second group of crack is carried out to modeling;

Path to the crack being associated with described Mitsui carries out modeling.

The method of 18. optimization fracture intervals according to claim 16, wherein analyzes the stress being associated with at least one crack of described first group and is at least net pressure based on expanding at least one crack of described first group.

The method of 19. optimization fracture intervals according to claim 16, wherein said first group and described second group of crack comprises at least two cracks and be isolated, make the crack being associated with described Mitsui in fact between first and second crack between first and second crack in described first group of crack and in described second group of crack.

The method of 20. optimization fracture intervals according to claim 19, it further comprises that the crack based on preventing from being associated with described Mitsui at least and described first group and described second group of crack intersect required spacing and determine the 3rd crack and the 3rd crack in the second crack and described second group of crack and the distance reducing between the second crack in described first group of crack, determines that described distance makes between second and third crack in described first group of crack and second and third crack in described second group of crack, not expand the second crack being associated with described Mitsui with described first group or described second group of crack crossing in the situation that.

The method of 21. 1 kinds of definite maximum horizontal pressure, it comprises:

Actual pressure during each pressure break stage of measurement rock stratum;

Determine the theory expectation pressure during each pressure break stage of described rock stratum;

At least comparison based on described theory expectation pressure and described measured actual pressure and determine the maximum horizontal pressure of described rock stratum.

Images