课件参考教程canada6-alex big guns environmental protection mini fracscaprock integrity

1、Environmental Protection through Mini-Fracs & other Caprock Integrity TestingPetro China Heavy Oil and Oil Sands Technologies Symposium, Sep. 5-6, 2012Big Guns Energy ServicesPresenter: Alex NemascuAuthor: Dickson LeeAgendaBackgroundCaprock IntegrityEnvironmental ImplicationsRegulatory ActionsIn-sit

2、u Stress TheoryStress Testing SolutionsMini-FracFracture Identification using Imaging ToolsBackgroundIn-situ oil sands extraction methods (e.g., cyclic-steam stimulation & steam-assisted gravity drainage) involve injection of steam, water, nitrogen or polymer into the bitumen-bearing sands reservoir

3、 at high pressuresUncontrolled releases of steam, oil or formation water to the surface or into aquifers create concerns for resource and environmental conservationWellReservoirCaprockAquiferSurfaceInjectorFractureFaultProducerInjectorFractureFaultEnvironmental ImplicationsIncident occurred in 2006

4、at Joslyn Creek SAGD site due to injections “at excessively high pressures”, causing a breach of the caprockCaused a surface disturbance about 125m x 75mRock projectiles travelled up to 300m horizontally from the main crater; plume of dust 1km long from the release pointNo loss of life or injuriesNo

5、 harmful gaseous emissionsRegulatory ActionsOngoing rewrite of ERCB Directive 051: Injection and Disposal Wells Well Classifications, Completions, Logging, and Testing Requirements to address thermal in-situ operationsDevelopment of specific application requirements to investigate caprock integrity

6、and max. operating bottomhole pressuresJoint study of oil sands caprock integrity Alberta Geological Survey from a geological & geomechanical perspectiveWhat is CaprockA non-permeable formation overlying a reservoir, acting as a barrier or seal preventing oil or gas migration to another subsurfaceMu

7、st display sufficient hydraulic and mechanical integrity to withstand max. injection pressures (with a factor of safety)CasingReservoirMain CaprockOther capping layersTypical Caprock Failure MechanismsCaprock fracture (tensile or shear failures)Fault reactivationPropagation of natural or pre-existin

8、g fracturesCement / casing failureModes of FractureMode I is pure tensile openingModel II is shear failure through sliding in the direction of the applied loadingMode III is a tearing, lateral, out-of-plane shear Complex or mixed-mode fracturing is commonCommon Caprock Integrity Assessment ToolsCapr

9、ock IntegritySimulation / ModelingLogsImagingMini-fracsCoringGeological InfoSeismicNatural Fracture SystemsFractures initiated at a wellbore may cut across a series of pre-existing natural fractures, or may begin propagating along an existing fracture parallel to the preferred stress orientation for

10、 fracture growthNatural Fractures IdentificationLogging Mechanical Rock Properties LMPChina Petroleum Logging Co. CPLEILogTM - Open Hole Logging and Borehole Imaging Conventional ToolsBorehole Imaging CPLs powerful imaging logging string: MCI-UITMCI: Micro Conductivity Imager UIT: Ultrasonic Imaging

11、 Tool - Fracture identification and characterization - Borehole breakouts - Structural Analysis and Formation anisotropy MCI UIT MCI - DynamicIn-Situ StressOpen-hole / Cased-hole LoggingCPLs MPAL-Multi Pole Acoustic Log: tc , ts . In - Situ Stress:Min. Horizontal Stress:HminMax. Horizontal Stress: O

12、verburden Stress From Conventional Logsperformed with CPLs ExCo4 Lithology & PorosityAcoustic Azimuthal Anisotropy Shear wave splitting:Slow ShearFast ShearHminHmaxMechanical PropertyElastic Modulus Poisson RatioCompressibility MPAL - Azimuthal AnisotropyOpen-hole / Cased-hole LoggingCasing integrit

13、y logs UIT Ultrasonic Imager: Cased Hole application- Internal corrosion imaging- Casing Deformation- Casing wall thickness based on acoustic diameters MFC - Multi Finger Imaging Tool- 40 80 Individual fingers- Focused Processing 3D ImagingRCBL Radial Analysis Cement Bond Log- Radial Bond Evaluation

14、 of Hydraulic Isolation - Casings up to 13.625 in 346mm - Tool centralized - riding on 30 wheels- Tool HZ conveyance: E- Coil or tractorMini-FracsA pulse injection test at a low rate into the test intervalBreakdowns the formation and creates a small fracture to establish communication with the true

15、formationDuring the shut-in period, pressure falls off and the fracture closesPressures are recorded during the injection and pressure-decline periods for analysisMini-Frac (contd)Fracture must cut through near-wellbore damage to provide good communication between the wellbore and the true formation

16、Breakdowns the formation and creates a short fracture, fractures are usually not create through the perforation channelsTo determine the formations min. in-situ stress Which in turn, determines maximum injection pressure during injection processes such as waterflood, SAGD or CSS while preventing fra

17、cture propagation into bounding layersTunnel created by perforatingFormationCementCasingIn-situ Stresses TheoryIn-situ earth stresses include:Stresses caused by overburden weightStresses caused by tectonic movementsStresses caused by creep flow and plasticityStresses caused by pore pressure and its

18、variationsPrincipal stresses have 3 orthogonal components (1, 2, 3)Let 1 = Sv (vertical or overburden stress) The other two principal stresses must be oriented horizontally, one larger and one smaller (2 = SHmax) and (3 = SHmin)In a mini-frac, the fracture naturally follows the path of least resista

19、nce, opening in the direction of the smallest principal stressIf Sv SHmin, fracture is verticalIf Sv wellbore hoop stress - formation breakdownWe use high-rate breakdown to e near-wellbore frictionInstantaneous Shut-in Pressure:The pressure immediately after pumps are shut downPressure drop after sh

20、ut-in due to friction in wellbore and the perforationsFracture Extension (or Propagation) Pressure:The minimum pressure which causes extension of a fractureRemains almost constant at constant rate injectionFracture Closure Pressure:Immediately before closure happens, fluid begins leaking from the fr

21、acture into the formationThe pressure required to hold the fracture open, also the pressure required to keep the fracture from just closingIt is taken as the min. in-situ stress acting normal to the fractureAfter-Closure Flow Regime:After closure the pressure transient established around the fractur

22、e propagates into the reservoir and transitions into linear, then pseudoradial flowMini-Frac Equipment DiagramPressures & TemperatureSurface real-time recorderDownhole real-time recordersW/R memory recordersInjection FluidClean KCL or HCL inhibited H2OPackoffHigh pressure wireline grease head packof

23、fReal-Time Surface RecorderReal-Time Downhole RecorderMemory Downhole RecorderInjection UnitConstant and controlled injection thru the use of specialized low rate injection units and the DCSSurface Recorders & MonitoringReal-time surface pressure, temperature & flow recorderReal-time monitoring in the injection unitHigh resolution and multi-redundancy monitoring system is critical to the success of mini-fracsMultiple pressure, temperature and flow measurements tak