Productivity Evaluation and Production Improvement of Offshore Low Permeability Oilfield: A Case Study of Xijiang Oilfield

doi:10.3969/j.issn.1006-396X.2021.05.007

Abstract

Abstract:

In view of the particularity of development, the lack of optimization and practice of production improvement measures for offshore low?permeability oilfields has led to severe challenges for its economic and efficient development. The research region is a typical offshore low?permeability oil reservoir, affected by the factors of nonlinear seepage, reservoir pollution, and strong constrained by unfavorable factors such as heterogeneity, which shows low productivity, rapid decline rate, and high?water content. Based on the productivity mathematical model combining porous media seepage theory and reservoir starting pressure gradient under multiple development methods, the production improvement effects of different development methods for the research region are predicted and compared in the actual geological conditions, which provides strong support for the optimization of production improvement methods, the formulation of reasonable development plans, and production deployment. The results show that the coincidence rate between the existing actual production data and equation calculation results is reached up to 85%. The development advantage of horizontal wells over vertical wells will decrease as the layer thickness increases. When the layer thickness exceeds 45 meters, the productivity ratio of these two wells is less than 5. For thin layer development, staged fracturing is suggested below 15 mD horizontal wells, but multilateral wells otherwise. This study will provide theoretical guidance and practical reference for the optimization of production improvement measures and development plan adjustments in offshore low?permeability oilfields.

Key words: Productivity equation, Low permeability, Offshore oilfield, Production measures

摘要：

鉴于开发特殊性，海上低渗油田的提产措施优选与实践较为缺乏，导致其经济高效开发面临着严峻挑战。目标区块属于典型海上低渗油藏，受非线性渗流、储层污染、强非均质性等不利因素制约，表现出产能低、递减率快、含水率高等特征。结合多孔介质渗流理论与油藏启动压力梯度，基于多种开发方式下产能数学模型，立足于目标区块实际地质情况，对不同开发方式的提产效果进行预测和比较，为提产措施优选、合理开发方案制定与生产部署提供有力支撑。结果表明，与现有生产数据对比，产能方程的符合率达到85%。水平井相对于直井的开发优势会随着层厚的增加而减弱，当层厚超过45 m时，二者产能倍比小于5。薄层开发时，建议15 mD以下采用分段压裂水平井，反之使用多分支井。研究结果将为海上低渗油田提产措施优选、开发方案调整提供理论指导与实践参考。

关键词: 产能方程, 低渗, 海上油田, 提产措施

CLC Number:

TE354

Qi Xiong. Productivity Evaluation and Production Improvement of Offshore Low Permeability Oilfield: A Case Study of Xijiang Oilfield[J]. Journal of Petrochemical Universities, 2021, 34(5): 43-49.

熊琪. 海上低渗油田产能评价与提产措施优选——以西江油田为例[J]. 石油化工高等学校学报, 2021, 34(5): 43-49.

Figures/Tables 10

Table 1 Experimental data of threshold pressure gradient

样品编号	孔隙度/%	渗透率/mD	启动压力梯度/(MPa $⋅$ m^-1)
1^#	6.753	0.007	10.600
2^#	11.384	0.213	0.310
3^#	16.745	0.721	0.034
4^#	13.177	1.225	0.019
5^#	12.289	1.667	0.019
6^#	19.962	15.500	0.018
7^#	14.245	62.500	0.015

Table 1 Experimental data of threshold pressure gradient

样品编号	孔隙度/%	渗透率/mD	启动压力梯度/(MPa $⋅$ m^-1)
1^#	6.753	0.007	10.600
2^#	11.384	0.213	0.310
3^#	16.745	0.721	0.034
4^#	13.177	1.225	0.019
5^#	12.289	1.667	0.019
6^#	19.962	15.500	0.018
7^#	14.245	62.500	0.015

Fig.1 Relation curve between permeability and starting pressure gradient in Xijiang oilfield

Table 2 Comparison of actual well production and that predicted from productivity equations in Xijiang oilfield

井号	储层厚度/m	渗透率/mD	生产压差/MPa	开发方式	实际产量/ (m³ $⋅$ d^-1)	计算产量/ (m³ $⋅$ d^-1)	绝对误差/%
XJ⁃1	13.3	3.3	11.0	定向井	9.0	9.7	7.8
XJ⁃2	28.8	78.6	8.7	压裂直井	196.1	211.2	7.7
XJ⁃3	24.7	91.0	3.8	压裂直井	98.5	93.4	5.2
XJ⁃4	28.5	12.1	11.8	压裂水平井	229.8	250.1	8.8
XJ⁃5	47.1	20.1	5.1	定向井	95.8	106.5	11.2
XJ⁃6	41.7	48.9	4.1	压裂直井	140.2	145.1	3.5
XJ⁃7	7.5	98.7	9.5	定向井	32.1	30.4	14.6
XJ⁃8	4.0	99.1	9.3	定向井	25.7	26.4	2.7
XJ⁃9	20.7	25.3	7.7	压裂直井	106.8	100.2	6.2
XJ⁃10	32.2	35.4	4.5	压裂水平井	114.5	106.5	7.0
XJ⁃11	27.7	6.5	12.1	定向井	50.2	44.5	11.4
XJ⁃12	19.2	12.8	12.1	定向井	46.6	46.4	0.4

Table 2 Comparison of actual well production and that predicted from productivity equations in Xijiang oilfield

井号	储层厚度/m	渗透率/mD	生产压差/MPa	开发方式	实际产量/ (m³ $⋅$ d^-1)	计算产量/ (m³ $⋅$ d^-1)	绝对误差/%
XJ⁃1	13.3	3.3	11.0	定向井	9.0	9.7	7.8
XJ⁃2	28.8	78.6	8.7	压裂直井	196.1	211.2	7.7
XJ⁃3	24.7	91.0	3.8	压裂直井	98.5	93.4	5.2
XJ⁃4	28.5	12.1	11.8	压裂水平井	229.8	250.1	8.8
XJ⁃5	47.1	20.1	5.1	定向井	95.8	106.5	11.2
XJ⁃6	41.7	48.9	4.1	压裂直井	140.2	145.1	3.5
XJ⁃7	7.5	98.7	9.5	定向井	32.1	30.4	14.6
XJ⁃8	4.0	99.1	9.3	定向井	25.7	26.4	2.7
XJ⁃9	20.7	25.3	7.7	压裂直井	106.8	100.2	6.2
XJ⁃10	32.2	35.4	4.5	压裂水平井	114.5	106.5	7.0
XJ⁃11	27.7	6.5	12.1	定向井	50.2	44.5	11.4
XJ⁃12	19.2	12.8	12.1	定向井	46.6	46.4	0.4

Fig.2 Adaptability of productivity evaluation method to the target block

Table 3 Yield increasing effect of different development methods

开发方式	预测产能/(m³ $⋅$ d^-1)	产能倍比	调研的产能倍比
定向井	32.1	1.0	1
水平井	145.2	4.5	2~5
鱼骨分型支井	170.6	5.3	4~15
多底型分支井	113.7	3.5	3~10
压裂井	184.1	5.7	3~9
分段压裂水平井	163.7	5.1	3~8

Table 3 Yield increasing effect of different development methods

开发方式	预测产能/(m³ $⋅$ d^-1)	产能倍比	调研的产能倍比
定向井	32.1	1.0	1
水平井	145.2	4.5	2~5
鱼骨分型支井	170.6	5.3	4~15
多底型分支井	113.7	3.5	3~10
压裂井	184.1	5.7	3~9
分段压裂水平井	163.7	5.1	3~8

Fig.3 Effect of layer thickness on productivity ratio of horizontal well and vertical well

Fig.4 Effect of permeability on productivity ratio of fishbone well and fractured horizontal well

Fig.5 Permeability distribution in target reservoir

Table 4 Optimization prediction of target reservoir of Xijiang oilfield

区块	油藏	渗透率/mD	厚度/m	流度/(mD $⋅$ m^-1Pa^-1 $⋅$ s^-1)	推荐井型	推荐提升技术	预期平均产量/(m³ $⋅$ d^-1)
A1	EP410	8.0~16.5	9.6	30.42~62.74	水平井	水平井分段压裂	378.7
A1	EP420	8.0~16.5	5.7	30.42~62.74	水平井	水平井分段压裂	220.6
A2	WC320 (I类储层)	>2.5	1.4~10.6	>7.00	水平井	水平井分段压裂	112.3
	WC320 (II类储层)	1.5~2.5	0.5~26.3	4.20~7.00	定向井	定向井水力压裂	70.9
	WC320 (III类储层)	<1.5	3.0~17.6	<4.20	水平井	水平井分段压裂	39.8

Table 4 Optimization prediction of target reservoir of Xijiang oilfield

区块	油藏	渗透率/mD	厚度/m	流度/(mD $⋅$ m^-1Pa^-1 $⋅$ s^-1)	推荐井型	推荐提升技术	预期平均产量/(m³ $⋅$ d^-1)
A1	EP410	8.0~16.5	9.6	30.42~62.74	水平井	水平井分段压裂	378.7
A1	EP420	8.0~16.5	5.7	30.42~62.74	水平井	水平井分段压裂	220.6
A2	WC320 (I类储层)	>2.5	1.4~10.6	>7.00	水平井	水平井分段压裂	112.3
	WC320 (II类储层)	1.5~2.5	0.5~26.3	4.20~7.00	定向井	定向井水力压裂	70.9
	WC320 (III类储层)	<1.5	3.0~17.6	<4.20	水平井	水平井分段压裂	39.8

Fig.6 Analysis on the effect of production enhancement in block A1

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