Interpretation of 3D Seismic and Subsurface data from the Buffalo ...
Interpretation of 3D Seismic and Subsurface data from the Buffalo ...
Interpretation of 3D Seismic and Subsurface data from the Buffalo ...
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<strong>Interpretation</strong> <strong>of</strong> <strong>3D</strong> <strong>Seismic</strong> <strong>and</strong> <strong>Subsurface</strong> <strong>data</strong> <strong>from</strong> <strong>the</strong><br />
<strong>Buffalo</strong> Valley Field, Chavez county, New Mexico<br />
S<strong>and</strong>eep Pyakurel, Thomas H. Wilson, Jaime Toro, <strong>and</strong> Shahab Mohaghegh<br />
Department <strong>of</strong> Geology <strong>and</strong> Geography, 419 White Hall, West Virginia University, Morgantown, WV 26506-6300<br />
Abstract<br />
Structure <strong>and</strong> isopach maps derived <strong>from</strong> formation top picks<br />
reveal <strong>the</strong> presence <strong>of</strong> differential subsidence across <strong>the</strong><br />
<strong>Buffalo</strong> Valley field during <strong>the</strong> Pennsylvanian <strong>and</strong> Permian<br />
periods. The <strong>Buffalo</strong> Valley field is located along <strong>the</strong> Northwest<br />
Shelf <strong>of</strong> <strong>the</strong> Delaware Basin. <strong>3D</strong> seismic <strong>data</strong> reveal that <strong>the</strong><br />
field is bounded by two normal faults, both <strong>of</strong> which drops to<br />
<strong>the</strong> sou<strong>the</strong>ast. The fault bounded block rotates slightly to <strong>the</strong><br />
sou<strong>the</strong>ast during deposition <strong>of</strong> <strong>the</strong> reservoir intervals.<br />
Production <strong>from</strong> <strong>the</strong> Morrow Formation is concentrated within<br />
this fault block. The Morrow production trend in this area is<br />
roughly north-south at an angle to <strong>the</strong> nor<strong>the</strong>ast trending<br />
Northwest Shelf in this area.<br />
<strong>3D</strong> seismic <strong>data</strong> volumes consisting <strong>of</strong> P-wave <strong>and</strong> PS-wave<br />
<strong>data</strong> are interpreted <strong>and</strong> compared in this study. VSP <strong>data</strong><br />
(zero <strong>of</strong>fset an some <strong>3D</strong> VSP coverage ) are incorporated into<br />
<strong>the</strong> seismic interpretation. The tie between surface seismic<br />
<strong>and</strong>s well-log derived syn<strong>the</strong>tics is generally poor due to<br />
Fresnel zone effects in <strong>the</strong>se heterogeneous intervals.<br />
Correlation <strong>of</strong> formation top depths to arrival times in <strong>the</strong> zero<strong>of</strong>fset<br />
corridor stack are used to identify reflection events in <strong>the</strong><br />
surface seismic <strong>data</strong>. In this study we examine <strong>the</strong> relationship<br />
<strong>of</strong> reflection amplitude <strong>and</strong> o<strong>the</strong>r seismic attributes associated<br />
with reflections <strong>from</strong> <strong>the</strong> Atoka-Morrow interval to 5- year<br />
cumulative production <strong>data</strong> <strong>from</strong> <strong>the</strong> field.<br />
Background<br />
The study area is located within <strong>the</strong> <strong>Buffalo</strong> Valley field in <strong>the</strong><br />
sou<strong>the</strong>rn part <strong>of</strong> <strong>the</strong> Chavez County, New Mexico (Figure 1).<br />
The area lies on <strong>the</strong> Northwest Shelf <strong>of</strong> <strong>the</strong> Delaware Basin.<br />
Production in <strong>the</strong> <strong>Buffalo</strong> Valley field is largely <strong>from</strong> a channel<br />
s<strong>and</strong> at <strong>the</strong> base <strong>of</strong> <strong>the</strong> Morrow Formation. Reservoir depth in<br />
<strong>the</strong> field is approximately 9000 feet subsurface. The Morrow<br />
Formation consists mostly <strong>of</strong> interbedded s<strong>and</strong>, shale <strong>and</strong> thin<br />
limestone deposits. The reservoir quality s<strong>and</strong>stone lies in <strong>the</strong><br />
lower part <strong>of</strong> <strong>the</strong> Morrow formation <strong>and</strong> is interpreted to be an<br />
inter-distributary channel fill deposit. The base <strong>of</strong> <strong>the</strong> Morrow<br />
coincides with <strong>the</strong> Mississippian unconformity. Channels at <strong>the</strong><br />
base <strong>of</strong> <strong>the</strong> Morrow scour into <strong>the</strong> Mississippian Barnett shale,<br />
which overlies <strong>the</strong> Chester Formation. The top <strong>of</strong> <strong>the</strong> Morrow is<br />
overlain by Atoka Formation which is comprised mostly <strong>of</strong> s<strong>and</strong><br />
shale <strong>and</strong> carbonate.<br />
Figure 1: Location map.<br />
<strong>Seismic</strong> <strong>data</strong> <strong>from</strong> <strong>the</strong><br />
<strong>Buffalo</strong> Valley area were<br />
provided by WesternGeco<br />
Syn<strong>the</strong>tic Tie<br />
The tie between reflection events <strong>and</strong><br />
formation tops was established at <strong>the</strong><br />
Read <strong>and</strong> Stevens, Inc., Lula #3 well (API<br />
No. 30-005-60481). Data available for <strong>the</strong><br />
Lula #3 include a near <strong>of</strong>fset VSP <strong>and</strong><br />
near <strong>of</strong>fset corridor stack (Figure 3).<br />
Arrival times <strong>of</strong> reflection events in <strong>the</strong><br />
surface seismic <strong>data</strong> were approximately<br />
44 milliseconds early relative to those in<br />
<strong>the</strong> VSP corridor stack. Wea<strong>the</strong>ring<br />
corrections <strong>and</strong> surface consistent static<br />
corrections are <strong>the</strong> likely cause <strong>of</strong> this<br />
difference.<br />
0.600<br />
0.700<br />
0.800<br />
0.900<br />
1.000<br />
1.100<br />
Trobough 1-A<br />
Lula3<br />
Bogle State Com 1<br />
6035 ft 4625 ft<br />
- Line 1034 + Corridor & Synth -<br />
SP: 1.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0<br />
A<br />
Wolf<br />
Cis<br />
Can<br />
St<br />
At<br />
1C<br />
2C<br />
Miss<br />
WDev<br />
0.600<br />
0.700<br />
0.800<br />
0.900<br />
1.000<br />
1.100<br />
Figure 3: Surface<br />
<strong>Seismic</strong>, VSP Corridor<br />
Stack & syn<strong>the</strong>tics<br />
Fresnel zone effects likely prevent a<br />
good match <strong>of</strong> syn<strong>the</strong>tic to corridor stack<br />
<strong>and</strong> VSP corridor stack to surface<br />
seismic. Some <strong>of</strong> this heterogeneity can<br />
be observed in <strong>the</strong> <strong>3D</strong> VSP <strong>data</strong> around<br />
<strong>the</strong> Lula #3 well (Right). The Fresnel<br />
zone radius at lower Pennsylvanian<br />
Morrow depths is approximately 1500<br />
feet using an RMS velocity <strong>of</strong> 16400 feet<br />
per second derived <strong>from</strong> <strong>the</strong> well velocity<br />
survey, <strong>and</strong> dominant frequency <strong>of</strong><br />
approximately 62.5 Hz. Given <strong>the</strong> <strong>3D</strong><br />
0.800<br />
0.900<br />
1.000<br />
1.100<br />
1.200<br />
SP:<br />
Lula3<br />
- Corridor Stack & Upgoing VSP -<br />
75.0 100.0 125.0 1.0 25.0 50.0 150.0 154.0<br />
Wolf<br />
Cis<br />
Can<br />
St<br />
At<br />
1C<br />
2C<br />
Miss<br />
WDev<br />
Figure 2: Zero Offset<br />
VSP & Corridor Stack<br />
Surface seismic <strong>data</strong> in <strong>the</strong> vicinity<br />
<strong>of</strong> <strong>the</strong> Lula #3 well (Figure 3) along<br />
with <strong>the</strong> near <strong>of</strong>fset corridor stack <strong>and</strong><br />
b<strong>and</strong>pass filtered syn<strong>the</strong>tic seismic<br />
traces compiled <strong>from</strong> <strong>the</strong> Lula #3<br />
sonic illustrate <strong>the</strong> seismic tie used to<br />
interpret reflection events. The east<br />
west inline 1034 is split at <strong>the</strong> Lula #3<br />
well. The corridor stack along with a<br />
series <strong>of</strong> b<strong>and</strong>pass filtered syn<strong>the</strong>tics<br />
have been inserted into <strong>the</strong> gap at<br />
<strong>the</strong> well location for comparison to<br />
surrounding seismic <strong>data</strong>. Formation<br />
top correlations to reflection events<br />
are illustrated. The section is quite<br />
heterogeneous at local scales, <strong>and</strong><br />
Lula3<br />
Line:<br />
Trace:<br />
1.000<br />
1.100<br />
2069.0<br />
10340.0<br />
St<br />
At<br />
1C<br />
2C<br />
Miss<br />
Figure 3: <strong>3D</strong> VSP<br />
VSP response, it is not surprising to see disagreement in <strong>the</strong><br />
details <strong>of</strong> <strong>the</strong> seismic response observed between <strong>the</strong> various<br />
<strong>data</strong> sets <strong>and</strong> <strong>the</strong> syn<strong>the</strong>tic seismogram. Based on <strong>the</strong> above<br />
comparisons we place <strong>the</strong> base <strong>of</strong> <strong>the</strong> Morrow (top <strong>of</strong> <strong>the</strong><br />
Chester) at 1.074 sec in <strong>the</strong> surface seismic. The reflection <strong>from</strong><br />
<strong>the</strong> top <strong>of</strong> <strong>the</strong> Atoka arrives at approximately 1.041 sec.<br />
1.000<br />
1.100<br />
0.800<br />
0.900<br />
1.000<br />
1.100<br />
1.200<br />
Figure 5: Type log for study<br />
area (Well 30005060321)<br />
Top <strong>of</strong> <strong>the</strong><br />
Atoka<br />
Top <strong>of</strong> <strong>the</strong><br />
Morrow<br />
Morrow Basal<br />
Channel<br />
Top <strong>of</strong> <strong>the</strong><br />
Barnet Shale<br />
Top <strong>of</strong> <strong>the</strong><br />
Chester<br />
<strong>Seismic</strong> time structure<br />
Time structure on <strong>the</strong> Chester <strong>and</strong><br />
Atoka reflection events (figures 6 <strong>and</strong><br />
7, respectively) reveals that <strong>the</strong> field is<br />
bounded along its western <strong>and</strong> eastern<br />
margins by two faults across which <strong>the</strong><br />
strata drop to <strong>the</strong> east. <strong>Seismic</strong> pr<strong>of</strong>iles<br />
<strong>from</strong> <strong>the</strong> <strong>3D</strong> survey (Figure 8) reveal<br />
that <strong>the</strong>se faults are nearly vertical.<br />
The isochore map for <strong>the</strong><br />
Atoka to Chester reflection<br />
events (Figure 9) suggests<br />
some movement along<br />
<strong>the</strong>se faults occurred during<br />
deposition <strong>of</strong> this lower<br />
Pennsylvanian interval.<br />
Log Response<br />
Formation top picks for most <strong>of</strong> <strong>the</strong><br />
wells were based on <strong>the</strong> gamma<br />
ray <strong>and</strong> density log response. The<br />
top <strong>of</strong> <strong>the</strong> Morrow (Figure 5) was<br />
generally difficult to pick but is<br />
<strong>of</strong>ten associated with a drop in<br />
density associated with <strong>the</strong><br />
predominantly clastic Morrow<br />
deposits. The basal Morrow<br />
channel is a low γ ray, high<br />
porosity zone that overlies <strong>the</strong> high<br />
Top <strong>of</strong> <strong>the</strong> Morrow<br />
γ ray Barnett shale (Figure 5)<br />
Basal Morrow<br />
Channel<br />
Figure 6: Time structure<br />
on top <strong>of</strong> <strong>the</strong> Chester Fm.<br />
Figure 7: Structure contour<br />
map: top <strong>of</strong> <strong>the</strong> Atoka Fm.<br />
Figure 8: <strong>Seismic</strong> pr<strong>of</strong>ile<br />
passing through <strong>the</strong> Lula #3<br />
well.<br />
Can – top <strong>of</strong> <strong>the</strong> Canyon<br />
Formation;<br />
St – top <strong>of</strong> <strong>the</strong> Strawn<br />
Formation;<br />
At – top <strong>of</strong> <strong>the</strong> Atoka<br />
Formation;<br />
1C – top <strong>of</strong> <strong>the</strong> Mississippian<br />
Chester Formation.<br />
Figure 9: Atoka to Chester<br />
Isochore Map.
Structure on <strong>the</strong> top <strong>of</strong> <strong>the</strong> Chester<br />
<strong>and</strong> Atoka formations is shown in<br />
Figures 10 <strong>and</strong> 11. In general <strong>the</strong><br />
structure follows <strong>the</strong> nor<strong>the</strong>ast trend<br />
<strong>of</strong> <strong>the</strong> Northwestern Shelf; however,<br />
north trending structural indentations<br />
interrupt <strong>the</strong> regional trend within <strong>the</strong><br />
field. Comparison <strong>of</strong> <strong>the</strong> time <strong>and</strong><br />
structure maps suggests that <strong>the</strong><br />
north trending faults observed in <strong>the</strong><br />
<strong>3D</strong> seismic <strong>data</strong> are probably<br />
associated with <strong>the</strong> structural<br />
indentation portrayed in <strong>the</strong> well<br />
derived structure maps.<br />
Figure 11: Structure on <strong>the</strong><br />
top <strong>of</strong> <strong>the</strong> Atoka Formation<br />
Structure & Isopach Maps<br />
Figure 10: Structure on <strong>the</strong><br />
top <strong>of</strong> <strong>the</strong> Atoka Formation<br />
Figure 12: Isopach map: top <strong>of</strong><br />
<strong>the</strong> Atoka to top <strong>of</strong> <strong>the</strong> Chester<br />
The isochore map <strong>of</strong> <strong>the</strong> Atoka to Chester top (Atoka through<br />
Morrow) reflection times (Figure 9) shows thickening along <strong>the</strong><br />
westernmost fault as well as across <strong>the</strong> sou<strong>the</strong>rn extent <strong>of</strong> <strong>the</strong> fault<br />
block in <strong>the</strong> survey area. The sou<strong>the</strong>rn part <strong>of</strong> <strong>the</strong> block appears to<br />
have rotated south-southwest during deposition, <strong>and</strong> at <strong>the</strong> same<br />
time <strong>the</strong>re appears to have been local subsidence across <strong>the</strong><br />
western fault that diminished to <strong>the</strong> north along its length. Reduced<br />
travel time differences observed in <strong>the</strong> Atoka-Morrow isochore to<br />
<strong>the</strong> north, along <strong>the</strong> trend <strong>of</strong> <strong>the</strong> western fault, show some similarity<br />
to <strong>the</strong> decreased thickness <strong>of</strong> <strong>the</strong> interval observed in <strong>the</strong> isopach<br />
map (Figure 12).<br />
The Atoko-Morrow isopach map (Figure 12) reveals that in <strong>the</strong><br />
nor<strong>the</strong>rn part <strong>of</strong> <strong>the</strong> <strong>3D</strong> survey area <strong>the</strong> Atoka-Morrow interval is<br />
over 100 feet thick, <strong>and</strong> increases to over 200 feet thick in <strong>the</strong><br />
south. The well derived maps provide a much coarser view <strong>of</strong> <strong>the</strong><br />
subsurface, with well spacing <strong>of</strong> about 2000 feet on average.<br />
However a pronounced trend <strong>of</strong> thickened Atoka-Morrow is clearly<br />
revealed along <strong>the</strong> trend <strong>of</strong> <strong>the</strong> seismic interpreted fault block.<br />
Future efforts will include conversion <strong>from</strong> timer to depth based on<br />
available sonic <strong>and</strong> well control <strong>from</strong> <strong>the</strong> field<br />
Production Data<br />
Five year cumulative production <strong>data</strong> <strong>from</strong> <strong>the</strong> <strong>Buffalo</strong> Valley field<br />
are shown in figures 13 <strong>and</strong> 14. Production <strong>data</strong> <strong>from</strong> two wells<br />
(highlighted in yellow) in <strong>the</strong> southwest corner <strong>of</strong> <strong>the</strong> area were<br />
omitted since production <strong>from</strong> <strong>the</strong>se wells was much higher (60471<br />
<strong>and</strong> 25725 Bbl ) than that in surrounding wells making it difficult to<br />
portray <strong>the</strong> production pattern on a linear contour scale when <strong>the</strong>se<br />
two wells were included. The average 5 year cumulative production<br />
obtained <strong>from</strong> 57 wells in <strong>the</strong> field is 4842.07 Bbl<br />
Figure 13: Oil production (units<br />
in barrels <strong>of</strong> oil)<br />
<strong>Seismic</strong> Attributes<br />
Figure 15: Average instantaneous<br />
frequency observed in a 0.014 sec<br />
window centered on <strong>the</strong> Morrow<br />
Figure 14: Gross s<strong>and</strong><br />
thickness within <strong>the</strong><br />
Morrow Interval<br />
Figure 16: Average instantaneous<br />
envelope observed in a 0.014 sec<br />
window centered on <strong>the</strong> Morrow.<br />
Preliminary attribute assessment suggests some relationship<br />
between spatial variations <strong>of</strong> instantaneous frequency (Figure 15) <strong>and</strong><br />
envelope (Figure 16) to production distribution. The average value <strong>of</strong><br />
<strong>the</strong> attribute was extracted <strong>from</strong> a 14 ms window centered roughly in<br />
<strong>the</strong> Morrow reflection event. A distinct channel-like pattern is not<br />
observed in <strong>the</strong> attribute maps. The productive Morrow s<strong>and</strong>s are<br />
generally less than 30 feet thick <strong>and</strong> are below <strong>the</strong> resolution limit <strong>of</strong><br />
<strong>the</strong> <strong>3D</strong> seismic <strong>data</strong>; however, areas <strong>of</strong> low instantaneous frequency<br />
coincide roughly with highs in <strong>the</strong> 5-year cumulative production within<br />
<strong>the</strong> survey area.<br />
P to S converted wave <strong>data</strong><br />
The <strong>3D</strong> seismic <strong>data</strong> set also includes a converted P to S wave<br />
volume. Side-by-side examples <strong>of</strong> <strong>the</strong> P-wave <strong>and</strong> PS-wave <strong>data</strong><br />
are shown below (figures 17 <strong>and</strong> 18 respectively). A pronounced<br />
zone <strong>of</strong> reduced amplitude is observed in <strong>the</strong> PS-wave <strong>data</strong><br />
volume that is not observed in <strong>the</strong> P-wave section. This zone <strong>of</strong><br />
low amplitude <strong>and</strong> reflection coherence may be associated with a<br />
narrow fracture zone (potentially gas filled).<br />
Figure 18: Display<br />
<strong>of</strong> P to S-wave<br />
<strong>data</strong> along pr<strong>of</strong>ile<br />
shown in Figure<br />
17.<br />
Figure 17: P-Wave<br />
seismic pr<strong>of</strong>ile<br />
through <strong>the</strong> Lula #3<br />
VSP well.<br />
Conclusion<br />
A tie between syn<strong>the</strong>tic <strong>and</strong> surface seismic proved difficult to<br />
establish. Comparison <strong>of</strong> well log derived syn<strong>the</strong>tics to <strong>the</strong> VSP<br />
near-<strong>of</strong>fset corridor stack was essential to identifying two-way<br />
travel times to formation tops <strong>and</strong> corresponding reflection events<br />
observed in <strong>the</strong> <strong>3D</strong> surface seismic. The response <strong>of</strong> <strong>the</strong> Atoka-<br />
Morrow intervals observed in <strong>the</strong> <strong>3D</strong> VSP confirms observations<br />
<strong>of</strong> <strong>the</strong> well log response in <strong>the</strong> field that <strong>the</strong> Atoka-Morrow interval<br />
is heterogeneous at interwell <strong>and</strong> seismic (Fresnel Zone) scales.<br />
The log response <strong>of</strong> <strong>the</strong> Morrow, is difficult to correlate <strong>from</strong> well<br />
to well whereas <strong>the</strong> top <strong>of</strong> <strong>the</strong> Chester Formation proved to be a<br />
more useful marker horizon.<br />
The <strong>3D</strong> seismic <strong>data</strong> <strong>from</strong> <strong>the</strong> field reveal that <strong>the</strong> play is<br />
bounded by nearly vertical faults that step down to <strong>the</strong> east. The<br />
faults are oriented roughly north-south at an angle to <strong>the</strong> NE<br />
trending shelf in this area. The eastern fault terminates to <strong>the</strong><br />
north while <strong>of</strong>fsets along <strong>the</strong> western fault decrease to <strong>the</strong> south.<br />
There appears to have been some movement along <strong>the</strong> faults<br />
during deposition <strong>of</strong> <strong>the</strong> Atoka-Morrow interval. Observable fault<br />
<strong>of</strong>fsets are located near <strong>the</strong> center <strong>of</strong> <strong>the</strong> field on <strong>the</strong> western fault<br />
<strong>and</strong> near <strong>the</strong> sou<strong>the</strong>rn end <strong>of</strong> <strong>the</strong> field along <strong>the</strong> eastern fault.<br />
Production <strong>from</strong> <strong>the</strong> Pennsylvanian Morrow Formation along<br />
<strong>the</strong> Northwest Shelf <strong>of</strong> <strong>the</strong> Permian Basin is generally confined to<br />
channel s<strong>and</strong>s at <strong>the</strong> base <strong>of</strong> <strong>the</strong> Morrow. These s<strong>and</strong>s are<br />
generally identifiable by low γ ray <strong>and</strong> high neutron porosity log<br />
response. Log derived structure <strong>and</strong> isopach maps reveal <strong>the</strong><br />
influence <strong>of</strong> <strong>the</strong> faults observed in <strong>the</strong> seismic. Structure maps<br />
clearly reveal that <strong>the</strong> field sits on an interruption in <strong>the</strong> regional<br />
trend <strong>of</strong> <strong>the</strong> Northwest Shelf. The Atoka-Morrow isopach reveals<br />
thickening <strong>of</strong> <strong>the</strong> Atoka-Morrow interval along <strong>the</strong> trend <strong>of</strong> <strong>the</strong><br />
fault block. Atoka-Morrow thickening increases <strong>from</strong> north to<br />
south suggesting that <strong>the</strong> fault block may have rotated to <strong>the</strong><br />
south during deposition <strong>of</strong> <strong>the</strong> Atoka-Morrow interval, consistent<br />
with observations made in <strong>the</strong> <strong>3D</strong> seismic <strong>data</strong> volume.<br />
Analysis <strong>of</strong> <strong>the</strong> P to S converted wave <strong>data</strong> suggests it will help<br />
identify additional faults or fracture zones within <strong>the</strong> field. Nearly<br />
vertical low amplitude zones appear in <strong>the</strong> P to S-wave <strong>data</strong> that<br />
could not o<strong>the</strong>rwise be easily identified in <strong>the</strong> P-wave volume.<br />
The analysis <strong>of</strong> seismic attributes <strong>and</strong> <strong>the</strong>ir correlation to<br />
production is in its early stages. Possible relationships between<br />
spatial variability in seismic attribute response <strong>and</strong> production<br />
<strong>from</strong> <strong>the</strong> Morrow channel will be examined in more<br />
comprehensive detail as <strong>the</strong> study continues.<br />
References<br />
Oil <strong>and</strong> gas fields <strong>of</strong> sou<strong>the</strong>astern New Mexico, Roswell Geological<br />
Society, 1999 & 1977 Supplements.<br />
Acknowledgements<br />
This research was funded through DOE/NETL contract DE-FC26-<br />
03NT41629. Our thanks to WesternGeco for providing <strong>the</strong> <strong>3D</strong><br />
seismic <strong>data</strong> <strong>from</strong> <strong>the</strong> area. The comments <strong>of</strong> Dave Oldham were<br />
greatly appreciated. Much <strong>of</strong> <strong>the</strong> well <strong>data</strong> were obtained <strong>from</strong> <strong>the</strong><br />
New Mexico Energy, Minerals, <strong>and</strong> Natural Resources Department<br />
Oil Conservation Division at http://ocdimage.emnrd.state.nm.us/.<br />
Production <strong>data</strong> used in <strong>the</strong> study were obtained <strong>from</strong> <strong>the</strong> New<br />
Mexico Tech “Go-Tech” site at http://octane.nmt.edu/<strong>data</strong>/ ongard/.