Page 211 - Basic Well Log Analysis for Geologist

LOG INTER PRYALATION CASE STUDIES

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Case Study 6
Devonian Hunton Formation
Anadarko Basin

Awell owned by your company has just reached final Recoverable volumetric gas reserves are calculated with
depth after penetrating its target zone—the Hunton these parameters: drainage area (DA) = 540 acres; gas
Formation in the Anadarko basin. The well was drilled gravity = 0,63 (estimated): temperature (estimated) =
because subsurface mapping indicated an updip fault and a 228°F: BHP (estimated) = 7,260 psi: recovery factor (RF)
structurally low well which produced gas and water. As you = 0.75; Z factor = 1.165. In addition, a geothermal
correlate logs from the newly completed well, you egradientof .014 x formation depth and a pressure gradient
determine that it is some 40 ft structurally high to the well of 0.445 x formation depth are used in reserve calculations.
which produced gas and water. You need to determine the following parameters: porosity

When your company’s well encountered the Chimney (@). water saturation (S,,), and reservoir thickness (h).
Hill Member of the Hunton Formation, a drilling break When the log evaluation is finished, you will make a
occurred. The penetration rate changed from [0 min/ft to 5 completion decision. And, if you decide to set pipe you will
min/ft, and the mud logger’s chromatograph increased 20 be responsible for selecting perforations. A Devonian
gas units. Hunton Log Evaluation Table (work Table F) helps organize
By examining samples, you identify Hunton lithology as the log data, but you must pick your own depths for
dolomite with some minor chert. [tis gray to gray-brown, calculation,
medium crystalline, and sucrosic with vuggy porosity.
Samples collected through the drilling break do not exhibit
fluorescence or cut.
Your usual procedure before beginning log analysis is a
check of Ry, values, generally known for the area, against a
log-calculated Ry value. This time, you decide to determine
a log value for Ry using charts (see Chapter IT) and the SP
log. The following information is assembled before you
begin finding an Ry value:

R,, Determination Using SP Log and Charts—You
determine SSP = —-95mv where the SSP value is read from
SP log: T; = 221°F: and Rye == 0.249 at Ty.
As youcxamine the log package on the new Hunton well.
you identify values for: resistivity of the mud filtrate (Ray =
0.249 at T;). surface temperature (70°F) and formation
(oy) before you determine neutron-density porosity,
temperature (22 1°F).
To correct neutron porosity for temperature in deeper
wells (generally over [2.000 ft) such as this Hunton well,
you need to add 1.5 porosity units (P.U.) to neutron porosity

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