WO2019148704A1 - 一种针对多煤层高地应力地区煤层气地质选区分析方法 - Google Patents

一种针对多煤层高地应力地区煤层气地质选区分析方法 Download PDF

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WO2019148704A1
WO2019148704A1 PCT/CN2018/088401 CN2018088401W WO2019148704A1 WO 2019148704 A1 WO2019148704 A1 WO 2019148704A1 CN 2018088401 W CN2018088401 W CN 2018088401W WO 2019148704 A1 WO2019148704 A1 WO 2019148704A1
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coal
dessert
area
coalbed methane
zone
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PCT/CN2018/088401
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French (fr)
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吴财芳
刘小磊
刘顺喜
杜明洋
张莎莎
张二超
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中国矿业大学
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Priority to AU2018308956A priority Critical patent/AU2018308956B2/en
Priority to CA3036466A priority patent/CA3036466A1/en
Priority to US16/337,411 priority patent/US11008859B2/en
Priority to ZA2019/02594A priority patent/ZA201902594B/en
Publication of WO2019148704A1 publication Critical patent/WO2019148704A1/zh

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    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B47/00—Survey of boreholes or wells
    • E21B47/06—Measuring temperature or pressure
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06Q—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES; SYSTEMS OR METHODS SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES, NOT OTHERWISE PROVIDED FOR
    • G06Q10/00—Administration; Management
    • G06Q10/04—Forecasting or optimisation specially adapted for administrative or management purposes, e.g. linear programming or "cutting stock problem"
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06Q—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES; SYSTEMS OR METHODS SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES, NOT OTHERWISE PROVIDED FOR
    • G06Q10/00—Administration; Management
    • G06Q10/06—Resources, workflows, human or project management; Enterprise or organisation planning; Enterprise or organisation modelling
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    • G—PHYSICS
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    • G06Q—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES; SYSTEMS OR METHODS SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES, NOT OTHERWISE PROVIDED FOR
    • G06Q10/00—Administration; Management
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    • G06Q10/06393—Score-carding, benchmarking or key performance indicator [KPI] analysis
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06Q—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES; SYSTEMS OR METHODS SPECIALLY ADAPTED FOR ADMINISTRATIVE, COMMERCIAL, FINANCIAL, MANAGERIAL OR SUPERVISORY PURPOSES, NOT OTHERWISE PROVIDED FOR
    • G06Q50/00—Information and communication technology [ICT] specially adapted for implementation of business processes of specific business sectors, e.g. utilities or tourism
    • G06Q50/02—Agriculture; Fishing; Forestry; Mining
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/006—Production of coal-bed methane

Definitions

  • the invention relates to a method for analyzing coalbed methane geological selection in a high-stress area with multiple coal seams, and belongs to the technical field of coalbed methane geological selection.
  • the geological constituency is the precondition for the development of coalbed methane. Only the first favorable coalbed methane development zone is expected to realize the large-scale overall development of coalbed methane. At this stage, China's geological selection criteria are mainly for the two single coal seam development basins in the Qinshui Basin and the eastern margin of the Ordos Basin. The focus is on the optimization of the plane enrichment and high permeability zone, and does not involve the problem of interlayer interference and vertical selection.
  • the eastern margin of the Qinshui Basin and the Ordos Basin is relatively simple, the coal structure is relatively intact, and the coalbed methane target layer is the main coal seam in the area, and the basic geological parameters are easy to obtain;
  • the geological conditions and coal seam occurrence conditions in the western Yunnan area are greatly different from those in the above two basins.
  • the main manifestations are that there are many coal seam layers in the area, up to several tens of layers, and the layer spacing is small, the coal seam single layer thickness is small, and the ground stress is high.
  • the invention designs an analysis method for coalbed methane geological selection in a high-stress area of a multi-coal layer in view of the deficiencies of the prior art.
  • the present invention adopts the following schemes: the three stages of the favorable area, the dessert area and the dessert section are sequentially selected, and the main steps are as follows:
  • a zone conducive to the development of coalbed methane as a favorable zone, preferably in a plurality of coal-bearing synclines; defining a zone that is advantageous for achieving high coalbed methane production as a dessert zone, one or several of the above preferred ones
  • the re-selection zone is limited to one coal-containing oblique interior; the vertical combination zone which is favorable for the development of coal-bed methane is defined as a dessert segment, which is vertically preferred within the range of the dessert zone;
  • the structural complexity is quantified by the fault fractal dimension
  • the ground stress is quantified by the structural curvature.
  • the coalbed methane resource quantity and the coalbed methane geological resource abundance in the favorable index of the favorable area have the right to one-vote veto.
  • the one-vote veto criterion is that the coalbed methane geological resources are less than 30 ⁇ 10 8 m 3 and the coalbed methane geological resources are abundant.
  • the degree is less than 0.5m 3 /km 2 ;
  • the structural complexity of the dessert zone has the right to one-vote veto.
  • the standard of structural complexity is one-vote veto.
  • the specific value is based on fault distribution and fault fractal dimension.
  • the corresponding relationship of the line graph is determined; the coal structure has a one-vote veto right in the preferred index of the dessert section, and the coal body structure one-vote veto criterion is that the proportion of crushed coal and glutinous coal is greater than 60%.
  • the key indicators are considered first, and then the reference indicators are considered. Among the key indicators, one vote is rejected first, and then other key indicators are considered; in the dessert zone optimization process, the priority of the key indicators is from high to low: Structural complexity, ground stress and burial depth; in the preferred process of dessert section, the priority of key indicators from high to low is: coal structure, critical desorption pressure difference and reservoir pressure gradient difference.
  • ⁇ is the density of the water column in the wellbore
  • g is the gravitational acceleration
  • ⁇ h is the height of the uppermost coal seam of the combined layer interval of the wellbore
  • ⁇ P cij is the critical desorption pressure difference of any two layers of coal in the combined interval.
  • i and j take 1, 2, 3..., i ⁇ j;
  • ⁇ W max is the maximum allowable reservoir pressure gradient difference in the combined interval, which can be determined by numerical simulation or field test.
  • ⁇ W ij is the reservoir pressure gradient difference of any two layers of coal in the combined interval, where i And j take 1, 2, 3..., i ⁇ j;
  • the invention has the following advantages and beneficial effects: forming a systematic and targeted selection analysis method for a special geological condition in a high-stress area of a multi-coal layer, which is progressive and interlocking, and can be fast It is effective to select suitable selection areas to provide theoretical support for the optimization of coal seam pressure cracking and drainage combination after the geological selection.
  • Figure 1 is a flow chart showing the execution of the method of the present invention
  • Figure 2 is a schematic view of a combined layer section in the preferred process of the dessert section
  • the present invention proposes a method for analyzing the geological selection of coalbed methane in a high-stress area with multiple coal seams.
  • the method of the present invention is preferably carried out in the order of the favorable region, the dessert region and the dessert segment, thereby obtaining the evaluation result.
  • the main steps of the method of the invention include:
  • the invention defines a favorable zone, a dessert zone and a dessert section: a zone which is beneficial to the development of coalbed methane is called a favorable zone, mainly refers to a “favorable oblique direction”, which is preferred among a plurality of coal-bearing synclines, and has a large area and a wide range.
  • the area that is conducive to the high production of coalbed methane is called the dessert zone, mainly refers to the “favorable construction zone”, which is preferred in one or several of the above-mentioned preferred zones, and the re-selection zone, the area and the range are small.
  • the dessert section which is vertically preferred within the scope of the dessert zone, mainly referring to the “favorable development interval”.
  • the order of the coalbed methane geological selection is: S1.
  • the favorable area is preferred, the S2. dessert area is preferred, and the S3. dessert stage is preferred.
  • the key indicators selected are coalbed methane geological resources, coalbed methane geological resource abundance and coalbed methane recoverable resources.
  • the reference index is 1km for shallow recoverable resources.
  • the key indicators selected are structural complexity, ground stress and buried depth, and the reference indicators are topography.
  • the key indicators selected are coal structure, critical desorption pressure difference and reservoir pressure gradient difference.
  • the reference indicators are the mechanical properties of coal seam and roof and floor.
  • the coalbed methane geological resources and the coalbed methane geological resource abundance have the right to one-vote veto, and the favorable area preferably includes the following sub-steps:
  • the geological resources of coalbed methane and the abundance of geological resources of coalbed methane are preferred. The higher the abundance of geological resources of coalbed methane and the geological resources of coalbed methane, the better the vote is rejected by one vote.
  • the one-vote veto standard is: coalbed methane
  • the geological resources are less than 30 ⁇ 10 8 m 3 and the abundance of coalbed methane resources is less than 0.5 m 3 /km 2 .
  • S102 The amount of recoverable resources of coalbed methane is preferred, and the higher the recoverable resources of coalbed methane, the better.
  • the reference index 1km is preferred for shallow recoverable resources, and the higher the shallow recoverable resources for 1km, the better.
  • the structural complexity has the right to vote for one vote, and the dessert zone preferably includes the following sub-steps:
  • the structural complexity is preferred, the simpler the structure is, the more complicated the one-vote veto is constructed.
  • the fault fractal dimension is quantitatively characterized. The larger the fault fractal dimension is, the more complicated the structure is. The area with particularly large fractal dimension is one-vote. The specific value is judged according to the correspondence between the fault distribution and the contour of the fractal fractal dimension.
  • S202 The ground stress is preferred. The higher the ground stress is, the more unfavorable. The maximum horizontal principal stress is greater than 18 MPa for the high ground stress region.
  • the structural curvature can be quantified according to the relationship between the structural curvature and the ground stress of the coal seam. Characterize the in-situ stress.
  • the buried depth is preferred, and the buried depth is preferably within the range of 800 m in the weathering zone, and the deeper the buried depth is, the more disadvantageous.
  • the coal structure has a one-vote veto right, and the dessert segment preferably includes the following sub-steps:
  • S301 The coal structure is preferred. The higher the proportion of primary structural coal and broken coal, the better. When the proportion of crushed coal and glutinous coal in a layer of coal is more than 60%, the coal is rejected by one vote. Vertical combinations are not considered.
  • the critical desorption pressure difference is preferably, and the coal seam is judged layer by layer according to formula (1):
  • ⁇ is the density of the water column in the wellbore
  • g is the gravitational acceleration
  • ⁇ h is the height of the uppermost coal seam of the combined interval of the wellbore initial liquid level.
  • ⁇ P cij is any two layers of coal in the combined interval. The critical desorption pressure difference, where i and j take 1, 2, 3, i ⁇ j.
  • ⁇ W max is the maximum allowable coal reservoir pressure gradient difference in the combined interval, with no inter-layer interference between coal seams as the standard, which can be determined by numerical simulation or field test
  • ⁇ Wi j is any two layers in the combined interval
  • the reference index is preferred.
  • the mechanical properties of the coal seam and the top and bottom plates mainly affect the extension of the fracturing crack.
  • the mechanical properties of the coal seam and the top and bottom plates are as close as possible, and the tensile strength of the top and bottom plates and the coal seam are The tensile strength is less than 5 times.
  • the difference in mechanical properties between the coal seam and the top and bottom plates is better.
  • the tensile strength of the top and bottom plates and the tensile strength of the coal seam are more than 5 times.

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Abstract

一种针对多煤层高地应力地区煤层气地质选区分析方法，包含以下步骤：定义了有利区、甜点区和甜点段的概念；选区过程按照有利区、甜点区和甜点段的顺序依次进行；针对每个阶段的特点选取不同的指标，在每个阶段明确提出了关键指标和参考指标，并在关键指标中给出了具有一票否决权利的指标；综合分析以获取所述的多煤层高地应力地区的煤层气勘探开发的有利平面区域及垂向层段。根据该方法，可以指导多煤层高地应力地区的煤层气地质选区，对于煤层气开发具有重要意义。

Description

一种针对多煤层高地应力地区煤层气地质选区分析方法 技术领域
本发明涉及一种针对多煤层高地应力地区煤层气地质选区分析方法，属于煤层气地质选区技术领域。
背景技术
目前，我国煤层气规模性开发主要集中在沁水盆地和鄂尔多斯盆地东缘，从“十三五”开始，开发区域逐渐向滇东黔西多煤层地区和新疆准噶尔盆地低煤级等地区扩展。滇东黔西地区作为我国煤层气勘探开发后备基地，具有丰富的煤层气资源，埋深在200～1500m的煤层气地质资源量达2.9×10 12m 3，具备规模性开发的资源条件。
地质选区是煤层气开发的前提条件，只有首先优选出煤层气开发有利区，才有可能实现煤层气的规模性整体开发。现阶段，我国的地质选区标准主要是针对沁水盆地和鄂尔多斯盆地东缘两个单煤层开发盆地，重点关注的是平面富集高渗区的优选，不涉及层间干扰和垂向选段的问题；相比滇东黔西地区，沁水盆地和鄂尔多斯盆地东缘构造相对简单，煤体结构相对完好，煤层气目的层均为该地区的主采煤层，基础地质参数容易获取；而滇东黔西地区地质条件及煤层赋存条件与上述两大盆地均有巨大差异，主要表现为该区煤层层数多，可达几十层，且层间距小，煤层单层厚度小，地应力高、构造复杂程度高和煤体结构破碎等，垂向上存在多个独立的含气系统，开发方式均为多层合层开发，不匹配的垂向层段组合会造成严重的层间干扰，致使产气量甚低。因此，在滇东黔西多煤层发育区进行煤层气地质选区时，不仅要进行平面有利区优选，而且要考虑垂向层段的组合优选。目前所选用的指标多为传统平面选区指标，缺乏代表性，且常常忽略了垂向有利层段评价指标。急需针对滇东黔西这种多煤层高地应力地区特殊地质条件形成一套系统的针对性强的选区分析方法。
发明内容
本发明针对现有技术的不足设计了一种针对多煤层高地应力地区煤层气地质选区分析方法。
本发明为实现以上目的，采用如下方案：按照有利区、甜点区和甜点段三个阶段依次进行优选，主要包括以下步骤：
1)将有利于煤层气开发的区域定义为有利区，在众多含煤向斜中进行优选；将有利于实现煤层气高产的区域定义为甜点区，在上述优选出的其中一个或几个有利区中进行优选，再选区，仅限于一个含煤向斜内部；将有利于煤层气开发的垂向组合层段定义为甜点段，是在所述甜点区的范围内进行垂向优选；
2)有利区的优选，其中，选取的关键指标为煤层气地质资源量、煤层气地质资源丰度和煤层气可采资源量，参考指标为1km以浅可采资源量；
3)甜点区的优选，其中，选取的关键指标为构造复杂程度、地应力和埋深，参考指标为地形地貌；
4)甜点段的优选，其中，选取的关键指标为煤体结构、临界解吸压力差值和储层压力梯度差值，参 考指标为煤层及顶底板力学性质差异。
进一步的，所述构造复杂程度通过断层分形维数量化，地应力用构造曲率量化。
进一步的，有利区优选指标中煤层气地质资源量和煤层气地质资源丰度具有一票否决的权利，一票否决标准为煤层气地质资源量小于30×10 8m 3且煤层气地质资源丰度小于0.5m 3/km 2；甜点区优选指标中构造复杂程度具有一票否决的权利，构造复杂程度一票否决的标准为断层密集发育区域，具体数值根据断层分布与断层分形维数等值线图的对应关系进行确定；甜点段优选指标中煤体结构具有一票否决的权利，煤体结构一票否决标准为碎粒煤和糜棱煤占比大于60％。
进一步的，优选过程中先考虑关键指标，后考虑参考指标，关键指标中先考虑一票否决指标，后考虑其他关键指标；甜点区优选过程中，关键指标的优先级从高到低依次为：构造复杂程度、地应力和埋深；甜点段优选过程中，关键指标的优先级从高到低依次为：煤体结构、临界解吸压力差值和储层压力梯度差值。
进一步的，甜点段优选指标中的临界解吸压力差值根据公式(1)来判断：
ρgΔh＞max|ΔP cij|   (1)
式中，ρ为井筒内水柱的密度，g为重力加速度，Δh为井筒液面距离组合层段最上面煤层的高度，ΔP cij为组合层段内任意两层煤的临界解吸压力差值，其中，i和j取1，2，3…，i≠j；
如果组合层段内煤层之间的最大临界解吸压力差值不满足公式(1)，则将临界解吸压力小的煤层去掉，继续判断，直到组合层段中的煤层间的最大临界解吸压力差值满足公式(1)为止；
甜点段优选指标中的储层压力梯度差值根据公式(2)来判断：
max|ΔW ij|＜ΔW max  (2)
式中ΔW max为组合层段内允许的最大储层压力梯度差值，可通过数值模拟或现场试验确定，ΔW ij为组合层段中任意两层煤的储层压力梯度差值，其中，i和j取1，2，3…，i≠j；
如果组合层段内煤层之间的最大储层压力梯度差值不满足公式(2)，则将储层压力梯度小的煤层去掉，继续判断，直到组合层段中的煤层间的最大储层压力梯度差值满足公式(2)为止。
本发明和现有技术相比，具有如下优点和有益效果：针对多煤层高地应力地区特殊地质条件形成一套系统的针对性强的选区分析方法，层层递进，环环相扣，可以快速有效的优选出合适选区，为地质选区之后即将进行的煤层气压裂和排采组合优化提供理论支撑。
附图说明
图1为本发明方法的执行流程图；
图2为甜点段优选过程中的一个组合层段示意图；
其中：1、煤层一，2、煤层二，3、煤层三，4、井筒，5、井筒中初始液面。
具体实施方式
以下将结合附图来详细说明本发明的实施方式，借此本发明的实施人员可以充分理解本发明如何应用技术手段来解决技术问题，并达成技术效果的实现过程并依据上述实现过程具体实施本发明。
为了有效解决多煤层高地应力地区煤层气勘探开发，本发明提出了一种针对多煤层高地应力地区的煤层气地质选区分析方法。本发明的方法按照有利区、甜点区和甜点段的顺序依次进行优选，从而获取评价结果。
本发明的方法的主要步骤包括：
本发明定义了有利区、甜点区和甜点段：将有利于煤层气开发的区域称为有利区，主要是指“有利向斜”，在众多含煤向斜中进行优选，区域大，范围广；将有利于实现煤层气高产的区域称为甜点区，主要是指“有利建产区”，是在上述优选出的其中一个或几个有利区中进行优选，再选区，区域和范围较小，仅限于一个含煤向斜内部；将有利于煤层气开发的垂向组合层段称为甜点段，是在甜点区的范围内进行垂向优选，主要指“有利的开发层段”。
接下来基于附图来详细描述本发明的方法的执行过程。
如图1所示，本发明中，煤层气地质选区的顺序为：S1.有利区优选、S2.甜点区优选、S3.甜点段优选。
S1：选取的关键指标为煤层气地质资源量、煤层气地质资源丰度和煤层气可采资源量，参考指标为1km以浅可采资源量。
S2：选取的关键指标为构造复杂程度、地应力和埋深，参考指标为地形地貌。
S3：选取的关键指标为煤体结构、临界解吸压力差值和储层压力梯度差值，参考指标为煤层及顶底板力学性质。
如图1所示，本发明提供的有利区优选关键指标中，煤层气地质资源量和煤层气地质资源丰度具有一票否决的权利，有利区优选中还包括以下分步骤：
S101：煤层气地质资源量和煤层气地质资源丰度优选，煤层气地质资源量和煤层气地质资源丰度越高越好，两者均低的一票否决，一票否决标准为：煤层气地质资源量小于30×10 8m 3且煤层气地质资源丰度小于0.5m 3/km 2。
S102：煤层气可采资源量优选，煤层气可采资源量越高越好。
S103：参考指标1km以浅可采资源量优选，1km以浅可采资源量越高越好。
如图1所示，本发明提供的甜点区优选关键指标中，构造复杂程度具有一票否决的权利，甜点区优选中还包括以下分步骤：
S201：构造复杂程度优选，构造越简单越好，构造特别复杂的一票否决，通过断层分形维数定量表征，断层分形维数越大构造越复杂，断层分形维数特别大的区域一票否决，具体数值根据断层分布与断层分形维数等值线的对应关系判断。
S202：地应力优选，地应力越高越不利，以最大水平主应力大于18MPa为高地应力区，在地应力数据不足的情况下，可根据煤层的构造曲率与地应力的关系，用构造曲率定量表征地应力。
S203：埋深优选，埋深处于风化带至800m范围内最好，埋深越深越不利。
S204：参考指标地形地貌优选，地形越平坦越好，可通过地表等高线的疏密程度进行定量表征。
如图1所示，本发明提供的甜点段优选关键指标中，煤体结构具有一票否决的权利，甜点段优选中还包括以下分步骤：
S301：煤体结构优选，原生结构煤和碎裂煤占比越高越好，当一层煤中碎粒煤和糜棱煤的比例占比大于60％时，该层煤一票否决，暂不考虑进行垂向组合。
S302：临界解吸压力差值优选，按照公式(1)对煤层进行逐层判断：
ρgΔh＞max|ΔP cij|   (1)
式中，ρ为井筒内水柱的密度，g为重力加速度，Δh为井筒初始液面距离组合层段最上面煤层的高度，如附图2所示，ΔP cij为组合层段内任意两层煤的临界解吸压力差值，其中，i和j取1，2，3，i≠j。
如果组合层段内煤层之间的最大临界解吸压力差值不满足公式(1)，则将临界解吸压力小的煤层去掉，继续判断，直到组合层段中的煤层间的最大临界解吸压力差值满足公式(1)为止。
S303：煤储层压力梯度差值优选，按照公式(1)对满足步骤S302中公式(1)的组合层段内的煤层进行逐层判断：
max|ΔW ij|＜ΔW max  (2)
式中ΔW max为组合层段内允许的最大煤储层压力梯度差值，以煤层之间无层间干扰为标准，可通过数值模拟或现场试验确定，ΔWi j为组合层段中任意两层煤的储层压力梯度差值，其中，i和j取1，2，3，i≠j。
如果组合层段内煤层之间的最大储层压力梯度差值不满足公式(2)，则将储层压力梯度小的煤层去掉，继续判断，直到组合层段中的煤层间的最大储层压力梯度差值满足公式(2)为止。
S304：参考指标优选，煤层及顶底板力学性质主要影响压裂裂缝的延展，当需要将煤层顶底板压穿时，煤层与顶底板的力学性质越接近越好，顶底板抗拉强度与煤层的抗拉强度在5倍以内，当不需要将煤层顶底板压穿时，煤层与顶底板的力学性质差别越大越好，顶底板抗拉强度与煤层的抗拉强度在5倍以上。
以上所述仅是本发明的优选实施方式，应当指出，对于本技术领域的普通技术人员来说，在不脱离本发明技术原理的前提下，还可以做出若干改进和变型，这些改进和变型也应视为本发明的保护范围。

Claims (5)

  1. 一种针对多煤层高地应力地区煤层气地质选区分析方法，其特征在于，按照有利区、甜点区和甜点段三个阶段依次进行优选，主要包括以下步骤：
    1)将有利于煤层气开发的区域定义为有利区，在众多含煤向斜中进行优选；将有利于实现煤层气高产的区域定义为甜点区，在上述优选出的其中一个或几个有利区中进行优选，再选区，仅限于一个含煤向斜内部；将有利于煤层气开发的垂向组合层段定义为甜点段，是在所述甜点区的范围内进行垂向优选；
    2)有利区的优选，其中，选取的关键指标为煤层气地质资源量、煤层气地质资源丰度和煤层气可采资源量，参考指标为1km以浅可采资源量；
    3)甜点区的优选，其中，选取的关键指标为构造复杂程度、地应力和埋深，参考指标为地形地貌；
    4)甜点段的优选，其中，选取的关键指标为煤体结构、临界解吸压力差值和储层压力梯度差值，参考指标为煤层及其顶底板力学性质差异。
  2. 如权利要求1所述的一种针对多煤层高地应力地区煤层气地质选区分析方法，其特征在于：所述构造复杂程度通过断层分形维数量化，地应力用构造曲率量化。
  3. 如权利要求2所述的一种针对多煤层高地应力地区煤层气地质选区分析方法，其特征在于：有利区优选指标中煤层气地质资源量和煤层气地质资源丰度具有一票否决的权利，一票否决标准为煤层气地质资源量小于30×10 8m 3且煤层气地质资源丰度小于0.5m 3/km 2；甜点区优选指标中构造复杂程度具有一票否决的权利，构造复杂程度一票否决的标准为断层密集发育区域，具体数值根据断层分布与断层分形维数等值线图的对应关系进行确定；甜点段优选指标中煤体结构具有一票否决的权利，煤体结构一票否决标准为碎粒煤和糜棱煤占比大于60％。
  4. 如权利要求1-3任一项所述的一种针对多煤层高地应力地区煤层气地质选区分析方法，其特征在于：优选过程中先考虑关键指标，后考虑参考指标，关键指标中先考虑一票否决指标，后考虑其他关键指标；甜点区优选过程中，关键指标的优先级从高到低依次为：构造复杂程度、地应力和埋深；甜点段优选过程中，关键指标的优先级从高到低依次为：煤体结构、临界解吸压力差值和储层压力梯度差值。
  5. 如权利要求4所述的一种针对多煤层高地应力地区煤层气地质选区分析方法，其特征在于：甜点段优选指标中的临界解吸压力差值根据公式(1)来判断：
    ρgΔh＞max|ΔP cij|    (1)
    式中，ρ为井筒内水柱的密度，g为重力加速度，Δh为井筒液面距离组合层段最上面煤层的高度，ΔP cij为组合层段内任意两层煤的临界解吸压力差值，其中，i和j取1，2，3…，i≠j；
    如果组合层段内煤层之间的最大临界解吸压力差值不满足公式(1)，则将临界解吸压力小的煤层去掉，继续判断，直到组合层段中的煤层间的最大临界解吸压力差值满足公式(1)为止；
    甜点段优选指标中的储层压力梯度差值根据公式(2)来判断：
    max|ΔW ij|＜ΔW max    (2)
    式中ΔW max为组合层段内允许的最大储层压力梯度差值，可通过数值模拟或现场试验确定，ΔW ij为组合层段中任意两层煤的储层压力梯度差值，其中，i和j取1，2，3…，i≠j；
    如果组合层段内煤层之间的最大储层压力梯度差值不满足公式(2)，则将储层压力梯度小的煤层去掉，继续判断，直到组合层段中的煤层间的最大储层压力梯度差值满足公式(2)为止。
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