﻿ 邻井随钻电磁测距防碰计算方法研究

1. 中石化胜利石油工程有限公司钻井工艺研究院, 山东东营 257000 ;
2. 石油工程教育部重点实验室(中国石油大学(北京)), 北京 102249 ;
3. 中国石油大学胜利学院油气工程学院, 山东东营 257061

A Method of Calculating of Avoiding Collisions with Adjacent Wells Using Electromagnetic Ranging Surveying while Drilling Tools
LI Cui1, GAO Deli2, LIU Qinglong1, KONG Xue3
1. Drilling Technology Research Institute of Shengli Oilfield Service Corporation, Sinopec, Dongying, Shandong, 257000, China ;
2. Key Laboratory for Petroleum Engineering of the Ministry of Education, China University of Petroleum(Beijing), Beijing, 102249, China ;
3. College of Petroleum Engineering, Shengli College, China University of Petroleum, Dongying, Shandong, 257061, China
Abstract: To eliminate the possibility of colliding with other wells in cluster wells, preliminary research has been performed to determine a ranging calculation method to avoid collision with adjacent wells using ranging electromagnetic surveying while drilling tools. Based on structure and fundamental principles of such electromagnetic tools, the magnetic source was regarded as a magnetic dipole to determine the distribution of magnetic fields around the magnetic source in accordance with the magnetic dipole theory. In this way, models for calculation of magnetic fields around the adjacent casing and intensity of magnetic induction around probe. In addition, the ranging calculation method of anti-collision while drilling by using electromagnetic anti-collision tools was established. Numerical simulation and other methods were adopted to determine the impact of parameters such as the magnetic source spacing inside the probe, the magnetic moment of magnetic source, the relative permeability of the casing, the diameter of casing, and the included angle between the drilling well and the adjacent well. It also included the magnetic induction intensity around the probe (positively correlated to spacing between sources), magnetic moments, relatively magnetic conductivity and diameter of casing, and other parameters. The proper design of key parameters of such tools could effectively enhance the intensity of magnetic induction around the probe and promote the accuracy of such tools. Research results showed that the newly developed ranging methods for avoiding colliding with adjacent wells while drilling by using electromagnetic tools could be used to determine the spacing and azimuth between the well being drilled and adjacent well in real time. These tools could basically satisfy demands for the drilling of cluster wells and may have great significance in the development of such anti-collision surveying tools.
Key words: cluster wells     adjacent wells     wellbore anti-collision     electromagnetic surveying     calculation method

1 邻井随钻电磁测距防碰工具结构与原理

 图 1 邻井随钻电磁测距防碰工具原理示意 Fig.1 Working principles of avoiding colliding with adjacent wells electromagnetic surveying while drilling tools

2个磁源磁极互相平行，发出的磁场方向相反(见图 1中绿线)。当探管周围没有套管存在时，由于2个磁源发出的磁力线方向相反，如果2个磁源的磁场强度一致，则在磁场传感器位置处2个磁源发出的磁场互相抵消，合成磁场为0。当探管周围有套管存在时，在套管位置2个磁源发出的磁力线在套管轴线上的分量方向是相同的，因此套管将会被这个磁场磁化产生沿套管轴向的磁场(见图 1中黄线)，该磁场被探管中间的磁场传感器探测到，进而得到相应的磁感应强度数据，然后通过丛式井邻井间距计算方法计算出正钻井与邻井之间的相对距离和方位，据此对正钻井井眼轨迹适当进行调整，以防止与邻井相碰。

2 丛式井邻井间距计算方法

2.1 磁源周围磁场分布规律

 图 2 磁偶极子示意 Fig.2 Schematic diagram of magnetic dipole

 (1)

a，dl用球坐标表示，代入式(1)后进行积分，

 (2)

 (3)

 (4)

 (5)

2.2 套管磁化磁场计算模型

 图 3 套管磁化磁场计算模型 Fig.3 Calculation model of magnetic intensity around casing

 (6)

 (7)

 (8)

 (9)

 (10)

P点的直角坐标为P(xyz)，由图 3可知，x=0，z=d+ytan α，将θ1r1θ2r2P点的直角坐标表示并代入式(10)，可得P点的微元被2个磁源磁化后的磁感应强度为：

 (11)

3 丛式井邻井距离计算

 (12)

 (13)

 (14)

 (15)

 (16)

 (17)

 (18)

4 邻井随钻电磁测距影响因素

4.1 磁源对测量结果的影响

 图 4 磁源间距对测量结果的影响 Fig.4 Effects of spacing between sources on measurement results

 图 5 磁矩对测量结果的影响 Fig.5 Effect of magnetic moment on measurement results

4.2 套管对测量结果的影响

 图 6 套管相对磁导率对测量结果的影响 Fig.6 Effect of relative magnetic conductivity of casing on measurement results

 图 7 套管直径对测量结果的影响 Fig.7 Effect of casing diameter on measurement results

4.3 正钻井和邻井夹角对测量结果的影响

 图 8 正钻井和邻井夹角对测量结果的影响 Fig.8 Effect of angle between drilling well and adjacent well on measurement results

5 结论与建议

1)  将磁源看作磁偶极子，根据磁偶极子附近的磁场分布，通过推导套管被磁源磁化后的磁感应强度计算公式和磁场传感器探测到的磁感应强度计算公式，可以得到邻井随钻电磁测距防碰计算公式。根据磁场传感器探测到的磁感应强度，可以计算出邻井距离。

2)  设计探管时，应使探管内的磁源间距达到1.2 m以上；对于选用材料为永磁铁的磁源，应尽量选用较大体积的产品，以使磁源的磁矩更大，达到更远的测量距离和更高的测距精度。

3)  套管的相对磁导率越大，探管探测到的磁感应强度越大，对工具的测距精度越有利。计算邻井距离前，需要对邻井套管的相对磁导率进行测量，得到较准确的相对磁导率才能保证测量结果有足够的精度。邻井套管的直径越大，系统探测到的磁感应强度越大，对系统测距范围和精度越有利。

4)  在正钻井和邻井的夹角不超过50°的情况下，邻井随钻电磁测距防碰工具可以获得较准确的测量结果；超过50°时系统测距精度较低，需要换用其他探测工具进行测量，以防止发生钻井故障。

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#### 文章信息

LI Cui, GAO Deli, LIU Qinglong, KONG Xue

A Method of Calculating of Avoiding Collisions with Adjacent Wells Using Electromagnetic Ranging Surveying while Drilling Tools

Petroleum Drilling Techniques, 2016, 44(5): 52-59.
http://dx.doi.org/10.11911/syztjs.201605009