The objectives of this three-phase study in the Harmattan–Elkton and Caroline areas of the Alberta Deep Basin are to understand the mechanisms behind drilling problems that have affected certain Cretaceous Ellerslie horizontal wells. Deliverables for Phase I include drilling summary plots for six wells at Harmattan–Elkton, the identification of drilling events in those wells, which would provide general insights into wellbore failure, pore pressure, minimum stress, characterization and diagnosis of drilling performance and problems, appropriate intervals for stress modelling and drilling mud weight recommendations. Phase II includes a review of mud weights used in the drilled wells, a determination of causes for steering issue problems, the influence of bit types on hole stability, an explanation of lost circulation in some intervals and calculation of breakdown pressures for hydraulic fracturing in new wells. Phase III provides drilling experience plots for four Ellerslie horizontal wells drilled in the Caroline area.