The Niobrara play in the Denver Julesburg basin is proving to be one of the more complicated horizontal shale oil plays within the industry. Multiple geologic challenges, such as complex normal faulting, basement tectonics, fractures, changing stress fields, highly uneven thermal maturities, and variations in reservoir quality have all contributed to the inconsistent production results experienced to date. Contributing to an already difficult set of geologic conditions, a wide range of horizontal drilling practices and procedures have also dramatically affected these irregular production results. Even in the so-called geologic " sweet spot" of the Niobrara in Wattenberg field, some of the early production rates have been disappointing, primarily because of drilling and completion practices.
Horizontal drilling in the Niobrara presents many technical challenges to operators and drilling engineers. These challenges range from building the curve in the Sharron Springs, changes to structural dip and extensive normal faulting along the length of the lateral, and reservoir/sweet spot variations within the multiple target chalk benches, to completion challenges related to well path orientation. Before drilling a well, many considerations must be precisely understood during the pre-planning phase of a horizontal drilling program. Such questions arise, like whether the operator should try to stay in zone and chase the faulted target, if one should geosteer-to-plan, drill toe-up, toe-down, if the faults hurt or help production, the orientation of the lateral, which benches will be the best targets, and, most importantly, how and where should one land the well? These issues are constantly evaluated by operators; however, economic success from these horizontal programs is often limited because of target-depth uncertainties associated with sparse well control, time-to-depth conversion of seismic information, and an apparent misunderstanding of the subsurface regarding reservoir sweet spots and stress fields. As an example, the B Chalk target in northern Weld County, Colorado is approximately 8% of the total thickness of the Niobrara and ~100 ft. below the unconformity surface, yet directional plans for this objective still tend to be based on Niobrara time structure horizons. This approach can be misleading when trying to accurately place a horizontal well in a thin chalk target.
Horizontal Well Planning
Extensive pre-planning for Niobrara horizontals, whether for a single well or a multi-well pad, is one of the most critical components of the drilling process. Pre-planning is key to successful geosteering, particularly when the geology is complex. Operators must know where the well is at all times to help ensure the bit remains in the target zone for thousands of feet, especially when drilling extended-reach wells. Additionally, the planning process anticipates exactly how the lateral is to be landed, where and when faults will be crossed, and how the stratigraphic dips change with respect to the angle of the bit. Careful pre-planning results in optimized completion staging and design and contributes to higher EURs.