Abstract

In 1956 at a Petroleum Engineering Conference at the University of Kansas Tixier presented an idea he called MAXIMUM PRODUCIBLE OIL INDEX [Y]. [Y] = (Rmf/Rxo)^0.5 – (Rw/Rt)^0.5

The [Y] represents the amount of oil per unit volume which is displaced by mud filtrate (Tixier, 1956), or to state it another way [Y] represent the difference in the water-filled porosity of the flushed (ɸrxo) and uninvaded (ɸrt) zones. Therefore using [Y] the geologist/engineer can determine Mobile So*ɸ*h without knowing porosity or RHS and then be able calculate Mobile OOIPstb.

Mobile OOIPstb = (7758*Y*h*Area)/BOI

The author decided to try to apply [Y] to three unconventional Permian reservoirs: 1.) Upper Avalon [Leonard] Shale, 2.) Upper Wolfcamp Shale, and 3.) 3^rd Bone Springs Sandstone. All three of these examples were logged with salt mud resistivity logs that exhibited hydrocarbon resistivity invasion profiles (LLD>LLS>MLL; or HRLA5>HRLA2>MCFL), which indicates these reservoir have undergone invasion. It is important to remember that without the reservoir having undergone INVASION the [Y] Method is INVALID. Therefore a limitation of the [Y] Method is that it will be limited to wells logged with salt mud resistivity logs, because invasion is difficult to verify in hydrocarbon-bearing reservoirs logged with fresh mud resistivity logs without having a MICROLOG.

RESULTS:

Permian Upper Avalon [Leonard] Shale: OOIPstb/160ac. = 19.1mmbo [Volumetric]

[Y calculated only if: LLD>1.2*LLS & LLS>MLL]

Mobile OOIPstb/160ac. = 2.4mmbo

Permian Upper Wolfcamp Shale:

OOIPstb/160ac. = 11.8mmbo [Volumetric]

[Y calculated only if: HRLA5>1.2*HRLA2 & HRLA2>MCFL]

Mobile OOIPstb/ac. = 2.2mmbo

Permian 3^RD Bone Springs Sandstone:

OOIPstb/160ac. = 5.4mmbo [Volumetric]

[T2>10ms 3.5mmbo T2>100ms 1.8mmbo]

[Y calculated only if: HRLA5>1.3*HRLA2 & HRLA2>1.2*MCFL]

Mobile OOIPstb/ac. = 1.9mmbo

Rylander and others, 2014 reported that “comparing recovery efficiencies computed from the free hydrocarbon volume is a superior way of comparing the effectiveness of hydraulic fracture stimulation”. If the [Y] Method is valid in evaluating unconventional reservoirs it would represent a free hydrocarbon volume similar using T2 cutoffs as outlined by Rylander and other, 2014.