Page 257 - Geology of Carbonate Reservoirs

238 SUMMARY: GEOLOGY OF CARBONATE RESERVOIRS

D
Thomlinson 18-1 Lott 18-1

18
19 6
Slaughter #3 Lott 19-9 Lott 19-12
Lott 19-2
1 Lott 19-1
Section 19 Block 2
5 10 15 20 25 25 20 15 10
T&N.O.R.R Co. Survey Lott 19-3
Garza Co., Texas Lott 19-11 Lott 6-1
Slaughter #6
Lott 19-4 Lott 19-3
Slaughter #4
Lott 19-13
1 5 10
Lott 19-7 10 5
N
Lott 10-5
Lott 19-6
Lott Trust #1
Lott 19-10
Lott 19-14
Dry Hole
Lott Trust #2 0 1,000
Producing Well
Feet Injection Well
Average Permeability for Interval
60-70 Feet Below Marker
Figure 8.14d (Continued).

in upper and middle parts of the buildup suggests that dissolution diagenesis occurred
soon after deposition and that it was most effective in the bathymetrically higher
part of the accumulation. If dissolution had been caused by deep - burial waters, it
should have been more extensive in the lower part of the reservoir, not the upper
part. However, there is more saddle dolomite in the lower part of the reservoir than
in the upper part, which may obscure the true nature of the predolomite pore geom-
etry. The extensive moldic and enlarged interparticle porosity in the oolitic grain-
stones was subsequently reduced by later diagenetic cements, including several
generations of calcite cement along with late - diagenetic anhydrite, saddle dolomite,
and chalcedony. These cements partially plugged the early porosity, but not in a sys-
tematic and stratigraphically predictable pattern. The absence of a clear pattern of
cement plugging has a negative effect on the correlation between measured porosity
and permeability (points on the φ – k plot are widely scattered). It was the mud -
shrouded packstones and rudstones stratigraphically below and interfi ngering with
the grainstones that became the reservoir rocks, probably because neomorphically
stabilized micrite in those beds reduced pore throat sizes and pore - to - pore connec-
tivity that partially shielded the muddy facies from the later cementation. As a con-
sequence, porosity and permeability in the rudstone – packstone facies correlate well
enough to allow estimates of permeability from the linear regression equation from
a φ – k plot. A surprise aspect about this reservoir is that the grainstone section is not