Hydraulic Integrity Research Articles

Semi-analytical models for stress change and fault reactivation induced by reservoir production and injection

A change in fluid pressure within a porous reservoir will generally induce stress changes within the reservoir and the rocks that surround it. Amongst the potential hazards resulting from these induced stress changes is the reactivation of existing faults or fractures, which may breach the hydraulic integrity of the caprocks that bound the reservoir. Fluid production and injection-induced stress changes in poroelastic media can be modeled using the theory of inclusions. Semi-analytical solutions of this type are presented in this paper for horizontal and dipping reservoirs of finite depth with rectangular and elliptical cross-sections, under plane strain conditions. Stress change parameters calculated using these equations are charted for different reservoir geometries and depths using dimensionless parameters, to facilitate their application to a broad range of reservoir depths and dimensions. Equations are also presented to assess the fault reactivation tendency resulting from induced stress changes using the Coulomb Failure Stress Change method. Fault reactivation analyses conducted for a horizontal reservoir of rectangular cross-section show that, during depletion, there is a tendency towards fault reactivation in the rocks near the lateral flanks of the reservoir, and within the central portion of the reservoir, in a normal fault stress regime. For a similar case in a thrust fault stress regime, there is a tendency towards fault reactivation in the rocks above and below the reservoir, but there is no tendency towards fault reactivation anywhere within the reservoir during depletion. It is also shown that fault reactivation potential is dependent on reservoir geometry and dip angle.

Geomechanical Factors Affecting Geological Storage of CO2 in Depleted Oil and Gas Reservoirs

Abstract A key to the success of long-term storage of CO2 in depleted oil or gas reservoirs is the hydraulic integrity of both the geological formations that bound it, and the wellbores that penetrate it. This paper provides a review of the geomechanical factors affecting the hydraulic integrity of the bounding seals for a depleted oil or gas reservoir slated for use as a CO2 injection zone. Potential leakage mechanisms reviewed include fault reactivation, induced shear failure of the caprock, out-of-zone hydraulic fracturing, and poorly sealed casing cements in enlarged, unstable boreholes. Parameters controlling these mechanisms include the upper and lower bounds of pressure and temperature experienced by the reservoir, the orientation and mechanical properties of existing faults, rock mechanical properties, in situ stresses, and reservoir depth and shape. Approaches to mitigate the likelihood of geomechanics-related leakage include the identification of safe upper limits on injection pressures, preferred injection well locations, review of historical records for reservoir pressures, temperatures and stimulation treatments, drilling program design to mitigate rock yielding in new wells, and assessment of wellbore integrity indicators in existing wells. Introduction In order to achieve significant reductions in the atmospheric release of anthropogenic greenhouse gases, the implementation of technologies to capture carbon dioxide (CO2) and store it in geological formations will be necessary. Deep saline aquifers have the largest potential for CO2 sequestration in geological media in terms of volume, duration, and minimum or null environmental impact(1). The first commercial scheme for CO2 sequestration in an aquifer is already in place in the Norwegian sector of the North Sea, where 106 tonnes of CO2 are extracted annually from the Sleipner Gas Field and injected into the 250 m thick Utsira aquifer at a depth of 1,000 m below the sea bed(2). In light of the economic benefits of enhanced oil recovery (EOR) derived from CO2 injection in oil reservoirs(3), these types of reservoirs will be attractive CO2 injection targets and, most likely, CO2 storage in depleted oil and gas reservoirs (or in conjunction with EOR) will be implemented before CO2 storage in aquifers. An advantage of CO2 storage in depleted oil or gas fields is the fact that much of the infrastructure for fluid injection (e.g., wellbores, compressors, pipelines) is already in place. The Weyburn CO2 Monitoring and Storage Project in Saskatchewan, Canada(4) is an example of a large-scale application of EOR operations using anthropogenic CO2, in which the oil reservoir is being evaluated for subsequent use as a long-term storage zone. A key to the success of long-term storage in depleted oil and gas reservoirs is the hydraulic integrity of both the geological formations that bound it, and the wellbores that penetrate it. The initial integrity of this "bounding seal" system is governed by geological factors. A considerable amount of effort has been devoted to the development of procedures for assessing fault seal capacity in potential hydrocarbon reservoirs(5).

Low-Risk TAML Level-5 Multilaterals in the South China Sea

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 88542, "Development of Low-Risk High-Level TAML Level-5 Multilaterals in the South China Sea," by Jonathan Park, SPE, and Duo Wei Shen, SPE, Baker Oil Tools, and Li Wen Yong and Yuan Fu Cun, ConocoPhillips China Inc., prepared for the 2004 SPE Asia Pacific Oil and Gas Conference and Exhibition, Perth, Australia, 18-20 October. The ConocoPhillips Xijiang fields in the South China Sea required multilaterals to increase oil production from the limited number of available platform slots. Further development in this area depended on slot recovery to maximize production and minimize hole collisions caused by frequent sidetracking in cluster wells. This paper discusses a method used to install low-risk multilaterals in these wells. This method reduced the risk and time associated with Technology Advancement of Multilaterals (TAML) Level-5 multilateral completions. This method eliminates the need for a high-risk-washover operation. Introduction The Xijiang fields, including the Xijiang 24-3 and Xijiang 30-2 fields and the Xijiang 24-1 satellite field, are approximately 130 km from Hong Kong. The fields are developed with two 24-slot platforms: Platform XJ 24-3 for Xijiang 24-3 field and Xijiang 24-1 satellite field, and Platform XJ 30-2 for the Xijiang 30-2 field. The Xijiang fields include multiple, laminated production sands from 1400 m true vertical depth subsea (TVDSS) to 2850 m TVDSS. The thickness of the production sands ranges from 1.5 to 92 m, with bottomwater or edgewater drive mechanisms. The porosity of the production sands ranges from 8 to 30%, and permeability ranges from 800 to 8000 md. The unconsolidated production sands require sand-control completions. The 24 drilling slots on Xijiang 30-2 plat-form were used up in March 2002; the 24 drilling slots on Xijiang 24-3 platform were used up in December 2003. The limitation of drilling slots significantly constrained the future development of Xijiang fields. To further develop the Xijiang fields, infill wells use sidetracking of existing wellbores. The first sidetrack for the Xijiang 30-2 field was initiated in March 1999; the first side-track for the Xijiang 24-3 field was initiated in June 1999; and the first sidetrack for the Xijiang 24-1 satellite field was initiated in July 2003. As of September 2004, a total of 39 sidetrack projects had been completed. Frequent sidetracking makes hole collisions a significant risk in Xijiang fields. To maintain daily oil production and increase ultimate recovery in the Xijiang fields, multilateral wells were adopted. Multilaterals reduce hole collision risks. When a well’s production decreases to its economic limit, it becomes a multilateral candidate. Because of the unconsolidated formation around the casing exit, hydraulic integrity and sand exclusion around the junction area in multilateral wells is critical. To optimize production, re-entry into the main bore is required for some sidetracks.

Geomechanical investigations into the hydraulic integrity of geological barriers

Geomechanical investigations into the hydraulic integrity of geological barriers

Geomechanical investigations into the hydraulic integrity of geological barriers

Geomechanical investigations into the hydraulic integrity of geological barriers

Sewer rehabilitation strategy in Berlin

Berlin Wasserbetriebe is in need of a significant and longterm investment in the rehabilitation of is sewer system. With ratification of the European Standard EN 752 Part 5, comprehensive rules have been set out for the rehabilitation of drain and sewer systems: hydraulic performance, environmental impact and structural integrity of complete catchment areas are given equal consideration. Taking this into account, Berliner Wasserbetriebe has developed a sewer rehabilitation strategy. Economic aspects are integrated with a cost-benefit-analysis; the significance of the remaining useful life of a pipe section is examined.

Large-leaved lime (Tilia platyphyllos) has a low ability to compartmentalize decay fungi via reaction zone formation.

• The growth of three basidiomycetes (Inonotus hispidus, Fomitopsis pinicola and Ganoderma adspersum) and one ascomycete (Ustulina deusta) was studied within the reaction zone (RZ) of large-leaved lime (Tilia platyphyllos) and host responses were compared with those formerly described in beech (Fagus sylvatica). The main objective of the study was to determine whether antimicrobial differences in host response and fungal growth within reaction zones exist. • The cell lumina in the RZ contained only sparse occlusions, which were easily degraded and did not prevent the passage of hyphae between adjacent cells via pits when RZs within excised wood blocks were challenged in vitro with the decay fungi. • In a comparison of extracts from the RZ of large-leaved lime and the stronger RZ of beech, differences were found in the concentrations and composition of induced antimicrobial compounds. The RZ of large-leaved lime was relatively weak, compared with the static RZ of beech, and migrated into the functional sapwood at an active microbial invasion front as a result of a dynamic interactive process. • These observations support previous interpretations that certain defence mechanisms in the xylem of trees are a means of maintaining hydraulic integrity, rather than physical and chemical barriers, which restrict or inhibit fungal growth.

Geochemical and microbial reactions affecting the long-term performance of in situ ‘iron barriers’

The in situ application of granular iron (Fe 0) has become popular for the destruction of halogenated organic compounds and for the immobilization of specific metals in groundwater. However, a knowledge gap exists concerning the long-term performance of the Fe 0-barriers. The corrosion of Fe 0 may produce mineral precipitates that alter the system’s hydraulic integrity. For example, data from existing barriers show varying trends in pH, alkalinity, mineral precipitation, and microbial activity. Although the chemical behaviors are site-specific, this paper discusses the concepts involved in developing a generic approach for predicting the trend of aqueous and surface speciation, and the resulting effects on Fe 0 treatment systems. Observations from existing Fe barriers are summarized, and the chemical and microbial processes that influence chemical speciation, both in water and on surfaces, are reviewed. A conceptual geochemical model is presented, which illustrates the factors that must be considered in developing a quantitative model that can be used to design monitoring plans for timely detection of clogging in Fe 0 reactive barriers. In order to develop quantitative predictive models, field and laboratory research should: (1) assess the extent and rates of media deterioration by analyzing coupled chemical and microbial reactions; and (2) identify the controlling mechanisms for hydraulic alteration within and around Fe 0 barriers.

Burst and Collapse of a Sealed Multilateral Junction: Numerical Simulations

Burst and Collapse of a Sealed Multilateral Junction: Numerical Simulations

Impoundment Liner Repair by Electrophoresis of Clay

Electrophoresis of clay particles from dilute suspensions is an innovative technology to seal leaks in operating surface impoundments that does not require removal of impoundment contents, exposure of workers to contaminants, or prior knowledge of the leak locations. A suspension of clay particles is added to the impoundment liquid. A cathode (negative electrode) is placed inside and an anode (positive electrode) is placed outside the leaking impoundment. A direct current (DC) electric field is imposed externally across the geomembrane liner through the leaks. The clay particles migrate to the leaks under the influence of the imposed electric field to form a clay cake seal. The results of laboratory experiments to evaluate the use of a DC electric field to direct migration of clay particles into a leak and the hydraulic integrity of the resulting seal are presented in this paper. The effects of clay type, clay particle concentration in suspension, size of leak, and electric field strength on the migration of clay particles and process of cake formation are evaluated. The sealing effectiveness and internal structure of the resulting clay cakes are examined by hydraulic conductivity measurements and nuclear magnetic resonance imaging. Electrophoretic mobilities of bentonite particles in different chemical environments were also measured to evaluate the feasibility of the technology in practical situations.

Geosynthetic Clay Liners Subjected to Differential Settlement

Geosynthetic clay liners (GCLs), which consist of a thin layer of bentonite attached to one or more geosynthetic materials, are receiving increased use as low-permeability barrier layers in waste-containment systems. Tests were performed in tanks to measure the hydraulic conductivity of GCLs that were subjected to differential settlement. In most cases the GCLs maintained a hydraulic conductivity of 1 × 10−7 cm/s or less when subjected to tensile strains of 1–>10%, depending on the material and test conditions. Overlapped GCL panels maintained their hydraulic integrity despite in-plane slippage of up to 25–100 mm. In general, the ability of GCLs to withstand differential settlement appears to be greater than that of compacted clay liners, but less than that of geomembranes. GCLs are a promising barrier material for situations in which differential settlement is expected, for example, in landfill final covers.

Modelling the contemporary stress field and its implications for hydrocarbon exploration

The forces that act on the Earth’s lithospheric plates are responsible for the stress regime within the plates at a regional scale, and thus influence issues pertinent to hydrocarbon exploration – such as the nature of fault reactivation, hydraulic seal integrity, natural and induced fracture orientation and wellbore stability. Four models of the intraplate stress field of the Australian continent have been produced by elastic finite element modelling of the forces acting on the Indo-Australian plate. All four models incorporate the push of mid-ocean ridges and of continental margins. In the four models the magnitude of the poorly constrained convergent boundary and basal drag forces are varied within reasonable limits. Despite being based on significantly different force magnitudes, regional stress orientations predicted by the three models that recognise the heterogeneity of forces acting along the convergent northeastern boundary of the Indo-Australian plate are considered reliable because they are consistent over much of the Australian continent and show broad agreement with the available in situ stress measurements.In the absence of in situ stress measurements, for example from borehole breakouts, modelled stress orientations should be incorporated into the assessment of issues pertinent to hydrocarbon exploration that are influenced by the contemporary stress field. In the context of fault reactivation, pre-existing vertical faults striking at 30° to 45° to the maximum horizontal stress direction are the most prone to at least a component of strike-slip motion. Planes dipping in the minimum horizontal stress direction are the most suitably oriented to be reactivated in extension, and planes dipping in the maximum horizontal stress direction are the most suitably oriented to be reactivated in compression. Modelled stress orientations can also be used to predict open natural fracture orientation, with the preferred orientation being normal to the minimum horizontal stress, and to help assess the hydraulic integrity of reservoir seals, with faults and fractures normal to the minimum horizontal stress least likely to be sealing.

Elastic buckling of cylindrical pipe linings with small imperfections subject to external pressure

Pipe linings are increasingly being used to extend the effective lifespan of pipe systems. A common situation arises when a thin-walled cured in place (polymeric) pipe is installed in a nominally cylindrical deteriorating gravity sewer to restore hydraulic integrity. Under these circumstances the prime structural requirement on the lining is to develop sufficient buckling capacity to resist the external head of groundwater pressure that usually builds up in the pipe-lining annulus. This paper develops a simple elastic buckling criterion for these systems assuming the constraint offered by the host pipe and surrounding ground can be considered as rigid, with small geometric imperfections between the host pipe and lining. The accuracy of the results obtained from the simplified analysis is demonstrated by comparison with those derived by a fully consistent formulation.

The influence of amendments on the volumetric shrinkage and integrity of compacted clay soils used in landfill liners

Clay liners remain an important component of composite liners used in landfill construction. Because their hydraulic integrity is frequently lost due to desiccation cracking, either during construction or shortly thereafter. The present study was initiated to evaluate the effects of common soil additives including lime, cement, and sand on the shrinkage and hydraulic conductivity of compacted clay soils commonly used in clay liner construction. Three soils having predominant clay minerals of smectite, illite and kaolinite were amended with varying amounts of lime, cement or sand; compacted using the Harvard miniature compactor; and the volumetric shrinkage was measured on the compacted samples. Additional samples of each treated soil were compacted according to ASTM 698 and used for measurement of the hydraulic conductivity. The results show that the majority of shrinkage occurs when the samples were dried to 25 °C with little additional shrinkage at temperatures up to 105 °C. The amendments of either 4% lime or 40 to 50% sand resulted in reduced shrinkage and increased hydraulic conductivity. The addition of 3% cement reduced shrinkage by up to 50% and simultaneously reduced hydraulic conductivity by 2 orders of magnitude. Thus, amendment of clay soils having a high shrink-swell potential with Type I Portland cement has the greatest poetential for field application as an amendment to help maintain the integrity and improve the long term performance of compacted clay liners.

Occurrence of decay‐associated xylem suberization in a range of woody species

AbstractSuberization responses to naturally‐occurring fungal colonization of living xylem tissues were detected in 30 of 37 woody species examined. These responses comprised the suberization of traumatic parenchyma tissues in compartmentalization wall 4 barrier zones laid down in the vicinity of fungally infected wounds, or the suberization of parenchyma cells, tyloses and vessel linings in reaction zone decay margins in fully differentiated sapwood. Additionally, in a few species, suberization of xylem fibres and tracheids was observed where juvenile xylem tissues, apparently still incompletely differentiated, had been exposed by wounding. These xylem suberization responses are considered to increase the decay resistance of the altered cells, and may protect the hydraulic integrity of adjacent tissue, thus contributing to the antimicrobial defence of the living sapwood.

Hydrochemical interpretation of groundwater flow systems in Quaternary sediments of southern Ontario

Shallow aquifer systems in surficial Quaternary sediments are geometrically complex, with highly variable hydraulic characteristics. Consequently these systems are extremely difficult to assess hydrogeologically using conventional investigation techniques and are often poorly understood. In a 500 km2 area of southern Ontario, hydrochemical techniques were used to investigate the hydraulic integrity and regional flow behaviour of 14 aquifer systems defined within 100 m of Quaternary overburden. This type of approach had been used successfully in more extensive bedrock aquifer systems but had not previously been applied on a regional scale to shallow Quaternary systems where sediment geochemistry and flow conditions are highly variable and rarely known. The study involved analysis of over 260 well waters for pH, major ions (Ca, Mg, Na, K, HCO3, Cl, and SO4) and subsidiary ions (NO3, I, Br, and F). Selected samples were analyzed for tritium.The groundwaters are classified into eight water types, two of which are sodium chloride in character and of bedrock origin. Of the remaining six, four are related by a chemical evolutionary sequence showing transition from a tritiated (> 30 TU), low-iodide (< 5 μg/L) CaHCO3 recharge water to an ion-exchanged, NaHCO3 water low in tritium (< 15 TU) and enriched in iodide (> 15 μg/L). The existence of this sequence implies a regional, composite flow system involving seven supposedly discrete aquifer systems.The two remaining water types are recent tritiated waters (> 20 TU) contaminated by road salt (Cl > 40 mg/L) and agricultural nitrate (NO3 > 10 mg/L). Together with the CaHCO3 waters these clearly delineate major areas of recharge and show that the covering of Halton Till is extensively permeable.