Exploration Insights December 2019/ January 2020

22 | Halliburton Landmark Exploration Insights | 23 Mid SNS Basin NS High Central WORDIAN CARBONIFEROUS KUNGURIAN MISSISSIPPIAN DINANTIAN SE N a S Flora Fm Boulton Fm Westoe Millstone Grit Brig Fm Flora Fm Cleaver U. Lmst. Fm Westoe Calster Fm Millstone Grit Bowland/ Edale Shale Fm Westoe Fm Millstone Grit Aeolian Playa lake Sabkha Uplands Bowland/ Edale Shale Fm Aeolian dunes Ephermal streams/ﬂuvial Sabka Playa lake b M. Lmst. Fm L. Lmst. Fm Screm. Fm Fell Sandst. Fm Zeeland Fm ? TOURNAISIAN ROAD. Leman Silverpit WUCHIAP. CHANGHS. GUADAL. NW SNS Basin South Cement- stone Fm Fluvio-deltaic Marine ﬁnes Carbonate platform Tayport Fm © 2019 Halliburton Continental Shallow marine Organic-rich sediment Low/moderate continental sand content Deep marine Interbedded clastics, coal and carbonate Fluvio-deltaics Marine ﬁnes Proximal ﬂuvio-deltaics Medial deltaics Carbonate platform c Figure 3> Chronostratigraphic diagrams of the Permian and Carboniferous in the Southern North Sea Basin. PREDICTING RESERVOIR QUALITY IN THE SOUTHERN NORTH SEA BASIN For the Permian, the porosity and permeability data from core align with the commercial field average values (for fields identified in Figure 2) down to around 3,000 m depth, below which the core data values tend to be lower. For the Carboniferous, the core porosity and permeability data are nearly all lower than their commercial field average counterparts. This could partly explain why the Carboniferous has largely been disregarded, but it may have more potential than first assumed. Besly (2018) believes that the Carboniferous interval has been overlooked and that potential gas discoveries have perhaps been missed in the way that the Breagh Field had been. Without further analysis and exploration, it is hard to distinguish whether the Carboniferous interval has under-delivered or if it has been under-explored. Mechanical compaction is the major porosity- reducing mechanism during burial, particularly between 2.5 and 3.0 km depth (Ramm, 1992). Below this, pressure solution at grain contacts, in combination with quartz cementation, degrades reservoir quality of most clean sandstones. This irreversible effect alongside the complex burial history of the Southern North Sea Basin may account for the anomalies seen in the porosity and permeability trends with depth (Figure 6), i.e. the uplift of rock units may have resulted in poorer quality reservoirs than expected for their present-day depths. For both the Permian and Carboniferous intervals, measured values from the undeveloped discoveries are similar to, if not better than, the predicted values you would expect using core-derived data in Figure 6. However, there are some discrepancies. The Eos and Glein undeveloped discoveries show porosity values that match our predictions, but poorer permeabilities. Both values are likely high enough Proximal ﬂuvio-deltaics Medial deltaics Distal deltaics Distal deltaics Turbidites d Fluvio-lacustrine Fluvio-deltaics Deltaics Uplands © 2019 Halliburton Uplands Fluvio-lacustrine Fluvial-deltaics Deltaics Figure 4> Gross depositional environment maps and their counterpart depositional environment block diagrams for (a) Rotliegend, (b) Visean, (c) Namurian, and (d) Westphalian.

Exploration Insights December 2019/ January 2020 | Page 22