﻿ 气顶底水油藏水平井垂向位置确定模型及应用

1. 中海石油(中国)有限公司天津分公司, 天津 300452 ;
2. 中国海洋石油国际有限公司, 北京 100010

The Model and Application in Determining the Vertical Position of Horizontal Well in Gas Cap and Bottom Water Reservoirs
ZHU Zhiqiang1, LI Yunpeng1, GE Lizhen1, TONG Kaijun2, YANG Zhicheng1
1. Tianjin Branch of CNOOC Ltd., Tianjin, 300452, China ;
2. CNOOC International Ltd., Beijing, 100010, China
Abstract: To control gas channeling and water coning, and to enhance development effect in oil reservoir, it is necessary to determine vertical positions of horizontal well accurately in gas cap and bottom water reservoirs. Based on the analysis of production characteristics of reservoirs with different bottom water and gas caps, a mathematical model has been derived for determining the vertical positions of horizontal wells that related to gas cap index, water volumes and reservoir pressures by using gas state equation and material balance equation, so as to establish the relationship among gas cap energy, bottom water energy and vertical positions of horizontal well in oil rim. The mathematical model can determine the reasonable vertical position of horizontal well in different gas cap and the bottom water reservoir to facilitate drilling operations. Numerical simulation and field application results showed that the technique had no restriction and requirement to the geometry of reservoir in determining vertical positions of horizontal wells in the oil rim in accordance with the gas cap index and water volumes, which possess a good adaptability for field applications.
Key words: gas cap     bottom water oil reservoir     horizontal well     vertical location     oil rim

1 气顶底水油藏垂向位置评价模型 1.1 模型的建立

 图 1 气顶底水油藏模式示意 Fig.1 Sketch map of reservoir with gas cap and bottom water

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1.2 模型的说明及用途

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α为0.5, 1.0和2.0时，分别表示水平井垂向位置为油环上1/3、中1/2和下1/3处。以压力为横坐标，水体倍数为纵坐标，得到气顶指数为0.8时水体倍数与压力的关系曲线(见图 2)。将实际气顶指数为0.8的油田的水体倍数(75倍)和压力(16 MPa)投影到图中，可以迅速判断出该油藏水平井合理的垂向位置为中1/2处。

 图 2 气顶指数为0.8时不同垂向位置处水体倍数与压力的关系 Fig.2 Relationship between the volume of water and pressure in different vertical positions with a gas cap index of 0.8

1)  对于气顶指数为0.5的小气顶油藏，当α为0.5, 1.0和2.0时，水体倍数与压力的关系曲线如图 3所示。从图 3可以看出：当水平井垂向位置为中1/2(图中黑线)处、油藏压力为15 MPa时，交点处(图中红点)对应纵坐标的水体倍数为80倍，即该水平井垂向位置条件下气顶指数0.5和水体倍数80能够使气侵和水侵同时到达井筒，此时气顶和底水能量平衡；当水体倍数大于80倍时，底水能量大于气顶能量，称为小气顶强底水油藏，水平井合理垂向位置为上1/3处，可有效控制气窜和水窜；当水体倍数为40~80倍时，称之为小气顶中等底水油藏，水平井垂向位置以中1/2处为宜；而水体倍数小于40时，称之为小气顶弱底水油藏，天然能量不足，水平井合理位置视注水情况而定。

 图 3 小气顶油藏水体倍数与压力的关系 Fig.3 Relationship between the volume of water and pressure in reservoirs with a small gas cap

2)  大气顶油藏的气顶指数为1.5，水平井垂向位置分别为中1/2处和下1/3处时，水体倍数与压力的关系曲线如图 4所示。

 图 4 大气顶油藏水体倍数与压力的关系 Fig.4 Relationship between the volume of water and pressure in reservoirs with a big gas cap

3)  考虑钻井过程中的容错性，以气顶指数大于1.5表示大气顶油藏，0.5表示小气顶油藏(中等气顶油藏可根据以上公式进行计算)，以水体倍数为40倍和80倍来区别强水体、中等水体和弱水体，可以得出：对于大气顶中等底水油藏，水平井垂向位置以中1/2—下1/3处为宜；对于大气顶弱底水油藏，水平井垂向位置以下1/3处为宜；对于小气顶强底水油藏，水平井垂向位置以上1/3处为宜；对于小气顶中等底水油藏，水平井垂向位置以中1/2处为宜。

4)  对于小气顶弱水体油藏，自身天然能量不足，一般采取注水开发，注水开发等效其水体接近刚性水驱(假设水体为100倍以上)，式(9)可变形为：

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 图 5 强底水油藏水平井垂向位置确定图版 Fig.5 Chart for determining the vertical position of horizontal well in strong bottom water reservoir
2 数值模拟验证

 图 6 不同类型油藏水平井垂向位置数值模拟结果 Fig.6 Numerical simulation results for vertical positions of horizontal wells in different types of reservoir

3 实例验证

X油田某油组气顶指数为1.5，水体倍数为30倍左右，为大气顶弱底水油藏，采用天然能量开发。根据前文研究，水平井垂向位置应为油环中下1/3处，但X1H井和X2H井在生产过程中却表现出不同的生产特征(见图 7图 8)。

 图 7 X1H井生产曲线 Fig.7 Production curve of Well X1H
 图 8 X2H井生产曲线 Fig.8 Production curve of Well X2H

X1H井生产平稳，初期未出现明显的气窜和水窜现象，说明水平井垂向位置合理；随着开发的进行，地层压力下降，生产后期以气窜为主，这与随着地层压力下降、水体倍数上升的认识是相符的。X2H井则过早出现水窜现象，与大气顶油藏生产特征不符。经构造重新精细解释，发现油藏内存在一条新断层，该断层将气顶能量进行分隔，导致X2H井附近气顶能量不足，成为小气顶油藏，故出现过早水淹状况。

4 结论

1)  基于气顶和底水能量的相对大小，运用物质平衡原理提出了一种确定气顶底水油藏水平井垂向位置的新方法。

2)  气顶底水油藏水平井的合理垂向位置主要取决于气顶和底水能量的相对大小，气顶能量大，则水平井在油环中的垂向位置应靠下；底水能量较大，则水平井在油环中的垂向位置应靠上。

3)  数值模拟及现场实例验证结果表明，水平井垂向位置确定方法能够指导气顶底水油藏水平井垂向位置优化和现场实施，但该方法在计算水侵量时忽略了时间因素的影响，对于水侵量计算方法明确的油藏仍具有局限性，可参考使用。

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#### 文章信息

ZHU Zhiqiang, LI Yunpeng, GE Lizhen, TONG Kaijun, YANG Zhicheng

The Model and Application in Determining the Vertical Position of Horizontal Well in Gas Cap and Bottom Water Reservoirs

Petroleum Drilling Techniques, 2016, 44(5): 104-108.
http://dx.doi.org/10.11911/syztjs.201605018