Advanced Water Injection for Low Permeability Reservoirs

Theory and Practice

Xinquan Ran

• Publisher: Gulf Professional Publishing
• Year: 2013
• Print ISBN: 9780123970312
• eBook ISBN: 9780123973214
• Topic: Physical Sciences
• Subtopic: Geology & Earth Sciences

Concise and readable, Water Injection For Low Permeability Reservoirs provides operators with the proper workflow systems and engineering techniques for designing, planning and implementing water injection systems that will improve recovery factors. When used in low permeability or ultra-low permeability reservoirs, water injection is one of the most economical methods for ensuring maximum production rates. This book provides both theoretical analysis and practical cases for designing and evaluating water injection systems and understanding key production variables involved in making detailed predictions for oil and water producing rates, water injection rates, and recovery efficiency.This book clearly explains the characteristics of ultra-low permeability reservoirs and linear flow theories. These topics are then applied to design and implementation. Application cases of four oilfields are included to help develop concepts while illustrating the proper workflow for ensuring waterflooding performance analysis and optimization. The book can be used as a reference for field technical personnel, or as technical support for the management personnel.- Discusses characteristics of low and ultra-low permeability reservoirs and linear flow theories- Provides detailed examinations of aspects such as stress sensitivity, fracturing timing, and nonlinear flow theory- Describes design and implementation of advanced waterflooding systems- Includes real case studies from four oilfields

Chapter 1

Features of Ultralow-Permeability Reservoirs in the Ordos Basin

Chapter Outline

1.1 Geological Features

1.1.1 Structural Features

1.1.1.1 Stress-Field Distribution

1.1.2 Sedimentary Features

1.1.3 Reservoir Features

1.1.3.1 Microfracture Features

1.1.3.2 Macroheterogeneity of Reservoirs

1.1.3.3 Microscopic Features of the Reservoirs

1.1.3.4 Reservoir Wettability and Sensitivity

1.1.3.5 The Temperature-Pressure Systems

1.1.3.6 Fluid Properties

1.1.3.7 Saturation of Movable Fluids

1.1.3.8 Features of Waterflood Efficiency

1.2 Features of Conventional Waterflooded Development

1.2.1 Water Absorptivity of Reservoirs

1.2.1.1 Waterflood Pressure

1.2.1.2 Index Curve Properties of the Injection Wells

1.2.1.3 The Entry Profile of the Injection Wells

1.2.2 Features of Oil Producer Responses

1.2.2.1 Features of Responses

1.2.2.2 Factors That Influence Well Responses

1.2.3 Features of Producer Deliverability

1.2.3.1 The Initial Deliverability

1.2.3.2 Patterns of Deliverability Changes

1.2.4 Changes in Productivity Indexes (PIs)

1.3 The Introduction of Advanced Water Injection Technology

1.3.1 Functions of Advanced Water Injection

1.3.1.1 Maintaining High Reservoir Pressure to Build an Effective Displacing Pressure System

1.3.1.2 Reducing Damage to Permeability Caused by Pressure Drop

1.3.1.3 Preventing Changes in the Physical Properties of the Oil in Place

1.3.1.4 Preventing the Flow Matrix from Being Plugged

1.3.1.5 Improving the Oil Permeability

1.3.1.6 Increasing the Sweep Efficiency of the Injected Water to Enhance Oil Recovery

1.3.1.7 Slowing Down Output Decline

1.3.1.8 Improving Producer Deliverability

1.3.1.9 Greatly Enhancing the Maximum Injector-Producer Distance and the Effective Coverage

1.3.2 Applicability of Advanced Water Injection

1.1 Geological Features

1.1.1 Structural Features

The second largest sedimentary basin in China, Ordos is a major cratonic-superimposed basin through long-term stable development over geological times, covering an area around 37×104 km² across five provinces, i.e., Shaanxi, Gansu, Ningxia, Inner Mongolia, and Shanxi. Its western margin lies in the junction between the Sino-Pacific tectonic domain in the east and the Techyan tectonic domain in the west. Its southern margin is close to the junction between the two giant geological units of North and South China. Its southwest margin is bounded by a deep fault, neighbored by the Qilian and Qinling fold systems. Its northwest margin is adjacent to the Alashan block, and the northern part is joined to the Inner Mongolian axis in the form of an island arc. The central part of the Basin lies in the west of the North-China platform in geological processes, and is also a part of the Sino-Korean paraplatform. Though it has experienced quite a few tectonic movements, the central part of Ordos lacks internal structures because these movements usually take place in the form of vertical lifting and subsidence of the platform as a whole. Its present structure is just a large westward-dipping monocline with a dip angle less than 1° and a gradient of only 6~8 m/km.

With reference to its current structural forms, the Basin can be divided into six first-order tectonic units, i.e., the Yimeng uplift, the Weibei uplift, the Jinxi scratch-fold belt, the Yi-Shaanxi slope, the Tianhuan syncline, and the thrust belt in the Western margin. The Yi-Shaanxi slope, containing a simple underground structure in the form of a large westward-dipping monoclinic with a dip angle less than 1°, developed a single type of reservoir, and therefore, became the mostly explored region with the most discoveries, including the upper and lower Palaeozoic gasfields and major oilfields with hundred million tons of oil, such as Ansai and Jing’an. This slope has thus become the main target of exploration and production in the Basin.

Decades of exploration and development, especially in-depth studies by generations of geologists, provide a general knowledge of distribution patterns of formations, structures, depositions, and resources within the Basin. In terms of hydrocarbon resource distribution, it is horizontally characterized by oil in the south and gas in the north, and vertically by gas in the lower formations and oil in the upper layers. According to regional tectonic evolution and sedimentary characteristics, the Basin has gone through five development phases: the aulacogen basin dominated by shallow marine clastic and carbonate rocks in the middle and late Proterozoic; the composite cratonic sag basin in which epicontinental carbonates are deposited in the early Paleozoic; the composite cratonic sag basin where coastal carbonates gradually transformed to clastic platform from the late Paleozoic to the middle Triassic; the sag basin where the large inland lakes and rivers deposit between the late Triassic and the Cretaceous; and the peripheral rift basin composed of inland river-and-lake filled rifts in the Cenozoic. These prototype basins, controlled by different tectonic movements, have both independent and interrelated evolution histories.

1.1.1.1 Stress-Field Distribution

An analysis of tectonic deformation traces and regional tectonic deformation characteristics within and around the Ordos Basin reveals that, after the sedimentation of the Triassic formations, the Mesozoic-Cenozoic tectonic stress field in the area can be divided into four stages, each with characteristics discussed as follows.

The Indosinian Period

Triassic Indosinian tectonic movements in the Ordos Basin produced an angular unconformity between the Jurassic and the Triassic, and parallel unconformity in other formations. The underlying layers, from the Carboniferous down to the Triassic, are linked in the form of conformity. According to the conjugate joints widely developed in the Carboniferous-Triassic strata along the Shanxi-Shaanxi boundary and the principal stress occurrence resulting from analysis of joints and microscopic rock fabrics within the Basin, the maximum principal stress axis in the Indosinian tectonic stress field is 10°∠2°, while the minimum is 100°∠3°. The middle principal stress occurrence is near vertical, a stress field with horizontally near north-south compression. An acoustic emission (AE) testing of the rocks from the Yanchang Group shows an average maximum effective principal stress of 93.5 MPa.

The Yanshanian Period

The Ordos Basin is dominated with mid-Yanshanian movements, with no obvious traces of early-Yanshanian movements. The large-scale uplifting of the eastern part in the late period of Yanshanian movements contributes to a structure of westward-tilting single dump in the Basin. Studies of the longitudinal bend folds, conjugate joints, initial sheet joints, shear zones, and microscopic rock fabrics in the Jurassic formations in the Basin and its surrounding areas show that the tectonic stress field during this geologic period has the maximum and minimum principal stress axes of 310°∠3° and 40°, respectively, while the middle principal stress axis is nearly vertical. The maximum principal stress axis calculated with statistics of the fracture occurrences observed at 45° along the Yanhe profile is 300°~310°∠5°, w...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Introduction
• Chapter 1. Features of Ultralow-Permeability Reservoirs in the Ordos Basin
• Chapter 2. Nonlinear Percolation Theory for Ultralow-Permeability Reservoirs
• Chapter 3. Design of Advanced Water Injection in Ultralow-Permeability Reservoirs
• Chapter 4. Technical Support for Advanced Water Injection
• Chapter 5. Practice of Advanced Water Injection
• Index