Eagle Ford Huff-n'-Puff (EOR) Single Well Pilot with Large Y-Grade Injection Volumes

Abstract The Eagle Ford at Chittim Ranch ("Chittim") in the Maverick Basin (Figure 1) has long been recognized as having a tremendous amount of oil-in-place. However, the combination of shallower depth, low pressure, and low API gravity have affected primary recoveries despite having OOIP per section of ∼68 MMBO. This can be observed through historical well results with low recovery factors and EUR’s of ∼40 MBO per 1000’. To unlock the true potential of this reservoir, BlackBrush began a 3-year study to design and implement an enhanced oil recovery ("EOR") project via a Huff n’ Puff ("HnP"). However, unlike many EOR/HnP projects that have been done to-date which utilize field gas, BlackBrush targeted another source of injectant; y-grade. Key advantages to y-grade over commonly used field gas include first contact miscibility, favorable relative permeability, as well as solvent benefits. Another key differentiator to other HnP projects is the ability to pump y-grade as a liquid (vapor pressure ∼450 psi) as opposed to field gas which generally requires large and expensive compressors to achieve minimum miscibility pressures. Anticipating that the injectant "containment" would be critical to success and project evaluation, a single isolated well was selected for the pilot with no direct offsets (except for a sister well at the heel). The pilot well had been producing for about 7 years and prior to the start of the HnP pilot was producing about 18 bbl/day. The production data, fluid properties, and fractures in the pilot area were used to develop a numerical model of the stimulated reservoir volume (SRV) for compositional simulation of the HnP process. The pilot was designed as a three HnP cycle test. Each cycle consisted of 15-30 days of injection and 30-60 days of production. Based on the compositional simulations, the SRV must be ‘re-filled" to at least a similar level of injectant volume in order to achieve the objectives of repressuring the reservoir, enhancing mass transfer, and remobilizing "dead" oil. A pump schedule was designed based on rate, pressure, and target injectant volume. BlackBrush then moved into the implementation phase and executed the pre-designed three cycles with outstanding results. At its peak in production cycle 3, the pilot well averaged over 1,000 bbl/day for a 5-day period. This represents a 50x increase in production from Pre-HnP levels. It is also worth noting that the historical initial production for this well (7 years earlier) was 760 bbl and only for a single day. This is the largest undertaking of a y-grade injection Huff-n'-Puff / EOR project known to the authors which hopes to progress the industries' learnings for EOR.