Strata: Wilrich and Falher Equivelents
WILRICH EXPLORATION STUDY RELEASE
Petrel Robertson Consulting Ltd. announces that the non-exclusive study "Regional Analysis and Reservoir Characterization of the Wilrich Member and Falher Equivalents, West-Central Alberta", is now available for viewing and purchase.
PRCL has created a systematic regional stratigraphic framework, based on data from >8000 wells, subdividing "Wilrich" productive trends into seven units over an area covering Twp 44-71, Rge 13W5-9W6. Each unit is mapped and analyzed in terms of production and exploration / development potential. Core logging, petrography, test analyses, quantitative petrophysics, and horizontal well completions analyses are essential parts of the investigation.
Liquids-rich Deep Basin reservoirs in west-central Alberta are highly prospective, even in the face of current low gas prices. One of the hottest plays being pursued in the basin targets the Wilrich Member and lower Falher submembers of the Lower Cretaceous Spirit River Formation. The first wave of intermediate production values shows rates of 2-25 MMCF/day of gas, with 5-70 bbl/MMCF of condensate plus liquids reported. Hot spots are appearing, and some areas have type curves showing stabilized deliverables of greater than 10 MMCF/day coupled with high gas-condensate and liquids production. While targeted horizontal drilling and multi-frac completions are attracting the most interest, Wilrich / lower Falher completions are also important in areas being developed using vertical wells with multi-zone completions.
Looking at the regional picture, Wilrich production is emerging as a number of isolated projects within a huge prospective fairway. Existing stratigraphic knowledge does not support clear mapping and understanding of reservoir facies and distribution, and the distribution of reservoir fluids and pressures on a regional basis is not clearly understood.
Petrel Robertson Consulting Ltd. (PRCL) has completed a regional stratigraphic study to support a better understanding of reservoir and fluids distribution within the Wilrich and lower Falhers, and we have analyzed drilling results to date in the context of this framework. Using this analysis, operators can both improve their exploitation of existing pools, and better assess new exploration and development opportunities.Summary
Our study area encompasses the entire Wilrich / lower Falher prospective fairway, defined as Townships 44-71 and Ranges 13W5 to 10W6 (Map 1). Key features bounding the fairway are the updip Deep Basin margin to the northeast, the Foothills deformation front to the southwest, the distal depositional limit of Wilrich / Falher sandstones to the northwest, and the proximal depositional limit of Wilrich / Falher marine sandstones to the southeast. Our analysis focuses on low-permeability sandstones of the Wilrich / lower Falher succession, and does not address hydrocarbon potential in equivalent shales.
Our initial task was the development of a clear and systematic sequence stratigraphic framework. Building on background knowledge from the literature and from PRCL's existing studies, we created a grid of regional stratigraphic cross-sections to define the overall geometry of the succession (Map 1). Relevant cores were identified and were logged with attention to identification of key surfaces as well as stratigraphic and sedimentologic features. Thin sections for petrographic analysis were prepared from selected core samples (see Appendix 3 for detailed procedures and results).
Next we pulled well logs from the approximately 31,000 penetrations of the Wilrich succession, in order to optimize mapping across the entire study area. We selected approximately 8000 wells using the following criteria:
- Targeted well density of about one well per section (where available) to support accurate characterization at a regional level;
- Greater focus and well density in hydrocarbon-saturated Deep Basin areas;
- Wells with relevant core, test, or production data;
- Horizontal wells targeting the interval of interest; and
- More recent wells with complete log suites including density tools.
Based on our core work and stratigraphic cross-sections, Wilrich and lower Falher units (submembers) were identified in each well. Eight stratigraphic horizons were picked (Falher F, G, H, I; Wilrich A, B, C; and the base Wilrich, or top of the Bluesky / Gething interval) and the net porous sands within the intervals were measured where log quality supported such picks. Clean sandstones are characterized by gamma log values of 60 API units or less; porous sandstones were picked using a 3% cutoff on a sandstone density log. These values were judged best for our regional mapping approach, with the assumption that most sandstones with these values would be capable of producing gas into a horizontal, multifrac'd wellbore (see further discussion in Petrophysical Evaluation chapter). Over 50,000 tops were picked, and over 40,000 net sand values measured. We followed with detailed mapping of individual submembers and the reservoirs preserved within each, including elements such as valleys, deltas, strand-plains and shelf-sands. We characterized facies, reservoir quality, and overall prospectively of these reservoirs based on detailed interpretive logging of core, supplemented by petrographic analysis. Interpretations were linked to well log signatures for efficient and comprehensive mapping.
When we undertook this project, we envisioned using sample cuttings extensively to assist in facies definition and reservoir assessment. This element of the study was not completed for two primary reasons:
- We had anticipated using about 5000 wells in the study originally, but went to about 8000 wells to adequately address stratigraphic characterization;
- Core and petrographic work demonstrated that while mineralogical and grain size variations exist within the Wilrich, they were less wide-ranging than anticipated, and thus sample cuttings work offered less additional information in terms of regional characterization than originally thought.
Detailed and systematic assessment of sample cuttings remains a critical element to understanding Wilrich prospectivity at the property / prospect scale.
Quantitative petrophysical analysis was undertaken on selected wells with core control and available digital (.las) curves. Our goal with this work was to demonstrate how well digital log data could characterize reservoir quality, as measured against core analysis values, and to recommend optimized workflows in quantitatively evaluating the Wilrich / lower Falher in newly-drilled and existing wells.
With the stratigraphic and depositional framework in place, test and production data were reviewed and assigned to the appropriate stratigraphic unit. Detailed procedures supporting hydrogeological analysis are reviewed in the Hydrogeology and Production Analysis chapter.
Operations data for wells that target Wilrich / lower Falher reservoirs were examined by our associated consultants at Fracknowledge to evaluate drilling and completions results. These data were linked with the stratigraphic framework to identify operational success in context of both stratigraphic controls and drilling / completions methodologies.
For more information contact:
Petrel Robertson Consulting Ltd.
500, 736- 8th Avenue S.W.
Phone: (403) 218-1618
Fax: (403) 262-9135