Opening mechanism of dynamic fractures caused by water injection and effective adjustments in low permeability reservoirs, Daqing oilfield in Songliao Basin

Wang Wenhuan; Peng Huanhuan; Li Guangquan; Lyu Wenfeng; Wei Chenji; Qin Yong

doi:10.11743/ogg20150517

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Opening mechanism of dynamic fractures caused by water injection and effective adjustments in low permeability reservoirs, Daqing oilfield in Songliao Basin
Vol. 36, Issue 5, Pages: 842-847(2015)
Online First：28 October 2015，

Published：2015
DOI： 10.11743/ogg20150517
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DOI：

Wang Wenhuan, Peng Huanhuan, Li Guangquan, et al. Opening mechanism of dynamic fractures caused by water injection and effective adjustments in low permeability reservoirs, Daqing oilfield in Songliao Basin[J]. 2015, 36(5): 842-847. DOI： 10.11743/ogg20150517.

摘要

大庆长垣外围低渗透油藏水驱开发受注水动态裂缝影响，水驱开发效果差。为改善水驱效果，需首先明确注水动态裂缝开启规律，进而才能提出开发调整对策。综合利用地质力学、油藏工程及数值模拟等方法，建立了注水动态裂缝开启压力计算方法，揭示了其开启机理和延伸规律，并针对裂缝开启不同情况，形成了相应的调整对策。研究表明：当注水压力超过储层现今最小水平主应力时，裂缝首先沿现今最大水平主应力方向开启；随着注水压力继续增加，裂缝沿与现今最大主应力方向夹角较小的注采井连线方向开启。根据裂缝开启压力计算方法，结合大庆外围A油藏条件，其裂缝开启的临界注水压力为9 MPa。油藏注水压力为12～14 MPa，当注水井排与现今最大水平主应力方向一致时，油藏沿现今最大水平主应力方向开启单方向裂缝，剩余油主要沿裂缝呈条带状分布；当注水井排与现今最大水平主应力方向呈一定夹角时，油藏开启多方向裂缝，剩余油被多方向裂缝切割呈零散分布。基于不同井网与裂缝匹配油藏剩余油分布模式，提出了“限压注水控制多方向注水动态裂缝开启、沿现今最大水平主应力方向裂缝线性注水、侧向基质驱替”的开发新理念，给出了注水压力界限与井网加密调整模式，现场应用效果显著。

Abstract

The performance of water flooding in low permeability reservoirs of Daqing oilfield is not satisfied due to the dynamic induced fractures.Understanding of the opening mechanisms of the dynamic induced fractures and optimization of development adjustment schemes are critical to improving water flooding recovery.Geomechanics

reservoir engineering and numerical simulation methods were utilized to establish a new method to calculate the fracture opening pressure and reveal propagation mechanism.Corresponding adjustment measures are proposed for different fracture opening scenarios.Results indicate that when injection pressure exceeds the current minimum horizontal principle stress

dynamic fractures will open first in the direction of the maximum horizontal principle stress.Then

they may open in the direction of line connecting injector and producer that has the smallest included angle with current maximum principle stress along with the rising injection pressure.Based on calculation methods of fracture opening pressure and in combination with the conditions of A reservoir in the periphery of Daqing oilfield

a critical injection pressure of 9 MPa is determined for fracture opening.Actually the injection pressure of A oilfield is up to 12～14 MPa.When the line of injection wells is in parallel with the current maximum horizontal principle stress

fractures only open in the direction of the maximum horizontal principle stress

and remaining oil are distributed along the fractures on both sides.Otherwise

fractures open in multiple directions

and the remaining oil distribute irregularly.Based on the remaining oil distribution under different well patterns

a new concept is proposed that 'controlling the opening of multi-directional dynamic fractures through limiting injection pressure and line flooding along the dynamic fracture in parallel with the maximum horizontal principle stress and lateral matrix displacement'.Water injection pressure limits and well pattern adjustment strategies are proposed under the gui-dance of this concept

and their field application is very successfully.