Our Montney clients often ask us: “What is the optimal/ideal for frac optimization?” Of course, this is a million-dollar question!
Montney is a very large play. The targeted play can reach up to 300-400 meters in thickness. Multiple subunits exist within the Montney play. Some subunits have been extensively developed and some remain still undeveloped. Many operators have started to tap on less developed areas and in some instances, results have been outstanding.
Montney wells usually require a large hydraulic frac job to fully realize their potential. The behaviour of frac growth and subsequent frac interactions in complex well configuration schemes combined with subtle geological and geomechanical environments is not fully understood. Fortunately, many Montney operators have started to adopt new surveillance techniques, such as micro-seismic mapping, downhole pressure monitoring systems, and stage-by-stage flow-backs in combination with fiber optics to better understand the frac behaviour.
One of the key drivers of frac behaviour which hasn’t received enough attention is the impact of geomechanics of the landing interval on the frac propagation. Montney usually exhibits substantial mechanical heterogeneity within all its subunits including the Upper, the Middle and the Lower Montney. Targeting the geomechanics sweet spots appears to be an important driver for frac optimization.
A few key questions to consider:
(1) How the geomechanics of the landing interval impacts the dynamics of out-of-zone frac growth, as well as the size of the stimulated rock volume and propped zones.
(2) How the geomechanics of the landing interval impacts the cluster efficiency and the conformity of the frac half length and frac height growth in multi-cluster plug and perf frac jobs.
There is extensive discussion in the unconventional rocks community about the best proxy to rank and evaluate the rock competency for frac optimization. Geologists have adopted traditional methods (widely used in porous and permeable conventional rocks) for unconventional tight rocks based on the geological characteristics, such as porosity, clay content, saturation, Total Carbon Content (TOC). Geomechanics use different approaches, such as Brittle Index (BI) or modified BI constructed from geomechanics logs and triaxial tests. Geophysicists use the mud rock line or Lambda-Mu-Rho (LMR) approach. Recently, some influencers have proposed using the minimum in-situ stress as the primary driver for hydraulic fracturing optimization. This begs the questions:
- Which proxy is the best to use?
- Can we define a universal approach to identify the optimal landing intervals acknowledging all disciplines including geology, geomechanics and geophysics?
In this blog, I will provide insights on how to use a new universal Mechanical Competency Index (MCI) to identity the geomechanical sweet spots. This will characterize fracability and how to optimize well placement with the Montney formation as a test case. In my earlier GLJ Insights Blog titled “New insights into shale fracability in Kaybob Duvernay,” we discussed this criteria and demonstrated the importance of the landing intervals.
Let’s look at the Montney formation as an example. Figure 1 illustrates the constructed MCI versus True Vertical Depth (TDV) for a three well pad in the liquid rich part of the Montney in British Columbia. Rocks are geomechanically more competent when this index is closer to zero.
Two wells are completed in the upper Montney (liquid rich) and one well in the middle Montney (leaner gas). The MCI is constructed by incorporating a broad range of available data including Diagnostic Fracture Injection Test measurements, dipole sonic and rock mechanics characterization.
As expected, non-reservoir formations such as Doig, Doig Phosphate, and Belloy are all geomechanically incompetent, creating potentially effective containment intervals for fractures completed in the Montney play. This is shown in the figure below in the dark blue colour in the colour bar. It is important to note that every rock can potentially break under the extensive forces generated by hydraulic fracturing. This is dependent on many factors including the proximity of the well to containment zones and size of the frac job, the frac pumping rate and the treatment pressure.
Figure 1: MCI (proxy for rock fracability) vs. TVD for an example of a three well pad in Montney, BC.
Clearly, Well A which is drilled closer to Doig/Doig Phosphate, is not optimally landed as the MCI has significantly deviated from frac initiation or the highest fracability line (note the light blue colour in this interval). This well has reported to have significantly grown out-of-zone and into the upper containment Doig and Doig Phosphate intervals.
Middle Montney Well C has landed in a low to moderately competent interval. This well has experienced many operational issues, such as proppant screen out and has required significant fluid and sand to be fraced. The operator has stopped placing wells in this zone due to operational difficulties and poor well performance.
How about Well B? At first glance, Well B has optimally landed in the most frackable interval. Let’s look at Well B’s directional survey to see if this well has stayed in the same competent rock all along.
Figure 2: Illustrates CMI along the well trajectory the (Black). The ISIP (Blue), average treatment pressure (Red), and directional survey (Green) are projected on the same plot for comparison.
Figure 2: MCI (proxy for rock fracability) vs. measured depth for an example of 3-well pad in Montney BC
As illustrated, a large portion of the lateral well, especially closer to the toe, has targeted a low to moderate geomechanics interval especially closer to the well toe. Note that the blue colour closer to the toe. This has been corroborated by larger Instantaneous Shut-in Pressure (ISIP) and treatment pressure closer to the well toe. Of course, one expects ISIP and average treatment pressure to be strongly correlated with the geomechanical competency/rock fracability. Higher ISIP and larger net frac treatment pressure can be an indication of lower frac quality within these interval.
You may ask: Why are some intervals in blue less frac competency and some in yellow high competency? What rock properties are the primary drivers?
A combination of various properties such as rock strength, rock stiffness, net effective stress (minimum stress subtracted by pore pressure), hardness and many other geomechanics parameters that are all integrated into MCI.
In the future, we will elaborate on the significance of targeting higher frac intervals for frac optimization in the Montney. For example, we will show that highest fracture intervals promote the creation of a larger lateral induced fracs, the better frac conformity during multi-cluster plug and perf jobs and even better frac containment. This can lead to lower chance of well-to-well interaction. This is especially true in the area where parent-child interaction is an issue, while accessing larger stimulated zones.
As Montney producers are adopting more advanced completion technologies, such as multi cluster plug and perf jobs targeting as many as 15 cluster per stage with Extreme Limited Entry (XLE) or Aggressive Limited Entry (ALE) perf in a complex well placement configurations optimized landing interval can increasingly improve the completion quality, and subsequently lead to better production well performance.
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