Article Figures & Data
Figures
- Fig. 1.
Lancaster Field: outline and location of well penetrations.
- Fig. 2.
Summary borehole data plot demonstrating cumulative PLT flow over the 205/21a-4Z basement interval. Cumulative PLT response for both DSTs indicate productive fractures are present throughout the logged interval.
- Fig. 3.
The three fracture end members (microfractures, joints and seismically identified faults) that comprise the Lancaster conceptual model. Dynamic data have been used to constrain the modelling assumptions applied to the fracture end members. As an example, the DFN model is a ‘snapshot’ of a modelled pressure response to the fracture and fault network, thus providing additional information on the fracture network properties away from the immediate wellbore environment.
- Fig. 4.
Lancaster conceptual reservoir model. Microfractures and joints are present throughout the Fractured Basement and Fault Zone facies. The conceptual model is intended to represent a continuum of connected fractures consisting of the three end members: microfractures, joints and faults.
- Fig. 5.
Evidence of porosity and permeability associated with microfracturing. (a) Microfractures as interpreted from FMI images. (b) Photographs of rotary sidewall core samples (RSWC). (c) Thin-section micrographs displaying rock fabrics interpreted from the RSWC noted in (b).
- Fig. 6.
Example of jointing identified from FMI and UBI images. A joint identified as a single sine-wave trace is represented by the red circled dip. Other joints can be seen in this figure characterized by sine waves of dark colour that cross the entire FMI and UBI images.
- Fig. 7.
Interpreted ranges of effective fracture apertures. Fractures (TS) represent fracture aperture ranges estimated from thin-section measurements. Joints reflect estimates of joint aperture ranges from manual estimates of borehole image logs corrected for fracture dip and borehole attitude. Veins (TS) represent widths of veins measured from thin section; and vein image logs represent vein widths estimated from FMI images. Note that veins are mineral-filled fractures and therefore do not contribute to reservoir porosity or permeability. The range of estimated fracture apertures is consistent with extremely high fracture permeability (Kair) and zero immobile water saturation (Sw) (Aguilera 1999).
- Fig. 8.
Summary of bulk porosity measurements and bulk porosity interpretation from LWD density neutron data recorded in the horizontal well. (a) Batemen–Konen-derived porosity (Bateman & Konen 1977) plotted against bulk density showing the relationship of bulk porosity to ‘litholines’ associated with sidewall core-derived grain densities representative of tonalite and dolerite bulk density ranges. (b) Bulk porosity averages split into Fault Zone facies and Fractured Basement facies. Facies thicknesses and percentage distribution is also noted. (c) Average bulk porosity for individual facies encountered in the horizontal basement section. Yellow bars represent Fault Zone facies; green bars represent Fractured Basement facies.
- Fig. 9.
Log data from 205/21a-6 across an interval of Fractured Basement and an interval of Fault Zone. Data presented (from left to right) are as follows: (1) Facies (Fault Zone (FZ)/Fractured Basement (FB)); (2) ROP; (3) gamma ray (red) and calliper (shaded); (4) LWD neutron-density (shaded) and PEF; (5) LWD resistivity; (6) LWD resistivity image; (7) LWD density image; (8) fracture interpretation; (9) Bateman–Konen porosity ( Bateman & Konen 1977); (10) C1/ROP; (11) GC tracer (high-resolution gas chromatography) total gas; (12) Flair (high-resolution gas chromatography) total gas; and (13) aromatic/alkane ratio. Insets are close-ups of image logs across the top and base of the Fault Zone.
- Fig. 10.
Summary rose diagrams comparing joint strike and joint statistics in Fault Zones and Fractured Basement in well 206/21a-6.
- Fig. 11.
3D representation of Lancaster facies model, displaying the base-case fault network as simulated in the dynamic model. The total number of faults is in excess of 700, the grid cell count is greater than 80 million.
- Fig. 12.
Workflow for constructing a static reservoir model. (a) Fault planes as interpreted from seismic. (b) Distance to fault property. (c) Fault-zone width property (40 m in this instance).
- Fig. 13.
Pressure derivative plot from 205/21a-6 DST data. The upwards inflection at the end of the derivative is interpreted to represent a dual porosity response, which can be visualized as two fracture sets contributing to flow (discrete fractures and non-discrete fractures). Note that fault planes are not explicitly modelled in reservoir simulation, their presence in the model is simply to provide a skeleton for placing Fault Zones.
- Fig. 14.
Sector model consisting of a 4×4 km sector model area in relation to the Lancaster Field. The sector model was undertaken in Eclipse to provide initial sensitivities on well orientation (inclined v. horizontal), potential aquifer strength and ‘Oil Down To’ (ODT).
- Fig. 15.
Extract from the Intersect full-field simulation model exhibiting a pressure drawdown snapshot over a particular reservoir depth in relation to the horizontal well. The modelled pressure response shows an isotropic distribution.
Tables
Resource STOIIP (MMstb) Recovery factory (%) Contingent resources* (MMstb) 1C 2C 3C 1C 2C 3C 1C 2C 3C Discovered conventional 143 258 411 20 29 39 28 74 161 Discovered unconventional 328 798 1665 10 16 17 32 126 276 Total discovered 470 1056 2076 13 19 21 60 200 437 *Contingent resources are based on the assumption that production facilities will operate with an 80% uptime.
The Lancaster Field: progress in opening the UK's fractured basement play
