﻿ 气体钻井最小气体体积流量计算新方法

A New Calculation Method of Minimum Gas Volume Flow Rate for Gas Drilling
Tang Jiatong
College of Earth Science, Yangtze University, Wuhan, Hubei, 430100, China
Abstract:Nowadays, gas injection rate for gas drilling is mainly calculated by means of Angel model, but its calculation results are frequently lower than the actual gas injection rates. Therefore, this paper firstly calculates the minimum flow rate necessary for cutting carrying based on the minimum velocity theory, and then calculates the minimum gas volume flow rate required for gas drilling by means of minimum kinetic energy method, the effects of gas flow rate and annulus cross-sectional area on the minimum gas volume flow rate in gas drilling have been analyzed, and particle group coefficient and resistance coefficient are introduced to correct the calculation results, so as to keep the minimum gas injection for gas drilling more accurate. The calculation results indicated that the corrected model is much more accordant with the practical situations than the Angel model, and the calculated minimum gas volume flow rate for gas drilling is greatly affected by the penetration rate and the borehole size.
Key words: gas drilling    pneumatic conveying    minimum gas injection    cutting carrying    particle group    Angel model

1 最小动能准则

2 Angel模型修正

Angel模型中，标准条件下气体的最小流速vgo是根据气体钻井实践得到的，在任何条件下都假设其为定值，这种假设会给计算结果带来误差。笔者将最小速度准则引入到Angel模型中，不再假设气体钻井所需最小气体流速为定值15.24 m/s，而是通过最小速度准则计算得到井内条件下所需的最小气体流速，然后将其转化为标准条件下的气体流速，并将该值赋予vgo，这样避免了Angel模型中因为选用固定最小气体流速对计算结果造成误差。同时，笔者还修正了Gray沉降末速度模型中的阻力系数，并引入了颗粒群系数。

2.1 气体最小流速准则

2.2 阻力系数

Angel模型中的阻力系数采用了Gray试验结果的平均值，但阻力系数受气体流量、环空截面积等因素的影响，如简单地选用Gray试验结果的平均值会对计算结果造成很大误差。根据气力输送理论[12]，对阻力系数进行修正。

2.3 颗粒群系数修正

3 最小注气量计算过程

 图 1 最小注气量计算流程 Fig.1 Calculation flow chart for minimum gas injection rate
4 实例计算与分析

Angel模型假设在任何条件下，气体钻井需要的大气条件下的气体最小环空流速都为15.24 m/s，然而在实际钻井过程中，机械钻速、岩屑直径和井身结构等都会对钻井所需的最小环空流速产生影响，假设所需的最小环空流速为定值会对最小注气量的计算结果造成误差。新模型通过引用阻力系数和颗粒群的阻力修正系数，将上述影响因素考虑进去，并可分析机械钻速、岩屑直径、井身结构对于最小注气量的影响。

4.1 机械钻速对于最小注气量的影响

 图 2 机械钻速与携岩所需最小环空流速的关系 Fig.2 The relation of the rate of penetration vs. the minimum annulus flow rate for cutting carrying

4.2 岩屑直径对于最小注气量的影响

 图 3 岩屑直径和最小气体流速的关系 Fig.3 The relation of cutting diameters vs. minimum gas flow rate

4.3 井身结构对于最小注气量的影响

 钻头直径/mm 气体流速/(m·s-1) 气体体积流量/(m3·min-1) 修正前 修正后 406.4 14.72 167.1 161.1 266.7 14.69 99.0 94.6 215.9 14.63 78.1 74.3

5 结 论

1) 引入最小速度准则对Angel模型进行修正,修正了气体最小速度采用定值而带来的计算误差；引入阻力系数和颗粒群修正系数对Angel模型进行了修正，并考虑了井身结构和环空中岩屑碰撞对气体钻井所需最小气体体积流量的影响。

2) 随着机械钻速增大，岩屑的产生速度不断提高，岩屑在上返过程中发生碰撞，导致钻井所需的最小气体体积流量不断增大。当机械钻速大于一定数值时，所需的最小气体体积流量要大于Angel模型的计算值。

3) 随着岩屑直径增大，实际所需的气体最小环空流速也增大。采用Angel模型计算时如不考虑岩屑直径的影响而简单地假设所需最小气体流速为定值，会对计算结果造成很大误差。

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#### 文章信息

Tang Jiatong

A New Calculation Method of Minimum Gas Volume Flow Rate for Gas Drilling

Petroleum Drilling Techniques, 2015, 43(04): 73-77.
http://dx.doi.org/10.11911/syztjs.201504013