Guest Editorial: The Challenge of Locating Maximum Bypassed Pay
Authors: Howard Allen 
Published: February 2015

Littered throughout the global oil industry are the wells, many of which were extraordinary producers, that ended their life cycles while still leaving 40% or more of the hydrocarbons in the ground. In the industry's heyday, these production shortfalls were not a major concern because of energy abundance. But as geoscientists actually began seeing a forthcoming end to the seemingly endless supply of oil and gas, finding more bypassed pay became a subject worth exploring. One technology that paid off was nuclear magnetic resonance (NMR), which made a quick leap from the medical field to the oil and gas industry in the early 1990s.

Concluding that NMR could be helpful in locating more hydrocarbons, the immediate challenge became how to best adapt it from its medical roots. At the outset, in the early days of this technology transfer, the answer focused on using NMR to measure how much free water and nonmoveable water was in a reservoir and determining permeability and producibility relationships between free fluid and permeability. With that knowledge in hand, correct irreducible-water-saturation resistivity measurements then could identify and quantify more definitively the amount of hydrocarbons in place.

A Technology's Development

But new technology rarely revolutionizes an industry overnight, and this was no exception. Most industries are not necessarily early adopters or effective integrators of change, whether organizationally or technologically, and the oil industry is not unique in this respect. At the same time, there is no doubt that both the upstream and downstream are highly innovative and certainly recognize the power of efficiencies and increased productivity. Locating "bypassed pay" should and does strike a collective corporate nerve.

In NMR's case, from the early 1990s to the present, an evolution of proprietary software and petrophysical analysis has gradually allowed for more use and better results. Initially, and still the backbone of today's more refined technology, NMR knowledge was applied to conventional well logs by using bound-fluid-volume and low-resistivity-pay models based on mineralogy, grain size, and pore geometry. Then, advanced modeling was joined with software relationships to produce synthetic magnetic-resonance-imaging logs, all of which could be done with or without magnetic-resonance data.

In other words, software was developed to generate essentially the output produced by a new openhole log. The upshot for operators was that they could virtually eliminate expensive logging and rig time, as well as tool availability issues. Just as important, operators could acquire more definitive data in wells that had already been logged, cased, and completed.

The process of modeling conventional-well-log data with a multimodeling software process has had the same objective over the years while being refined. That is, the final output should represent a comprehensive petrophysical process identifying all potential pay intervals. And those intervals should even include bypassed zones caused by myriad formation-evaluation problems.

As mentioned earlier, not every operator jumped on the bandwagon at the outset because of skepticism about the process and whether it made economic sense in the first place. When bypassed-oil recovery rates had increased total well production "only" to the low-80% recovery range, petrophysicists went back to the drawing board.