Reservoir Characterization
Using Production Performance
Case History: TXL Unit (West Texas)
Tom Blasingame
Department of Petroleum Engineering
Texas A&M University
College Station, TX 77843-3116
(979) 845-2292 —
TXL Unit Example: Introduction
The TXL (Clear Fork) Unit is a typical low per-meability, shallow-shelf-carbonate reservoir lo-cated in Ector County, TX. This reservoir has been under primary production at 40-acre spac-ing and was reviewed for infill/waterflooding.
Work to date—production data analysis:
Reserves were estimated using well logs
EUR Analysis: (q/p) versus Np
Decline Type Curve—Closed Reservoir
Mapping of reserve estimates and reservoir properties.
Comparison Plot: OOIPlog versus OOIPWPA
TXL Unit Example: Well TXL-S 5601—History
Oil flowrate is allocated based on periodic tests. The rate "stabilization" at approximately 1 STB/D is reasonable.
TXL Unit Example: Well TXL-S 5601—EURPI Plot
(q/p) trend decays rapidly (reflecting the rate-time de-crease)—this is probably a remediation candidate.
TXL Unit Example: TXL-S 5601—Data Edit Plot
An excellent trend of (q/p) vs. —virtually all of the data adhere to the dominant trend.
TXL Unit Example: TXL-S 5601—WPA Plot
Excellent match—skin factor indicates significant stimula-tion. From EUR analysis, late-time production decay sug-gests remediation, WPA indicates minor deviation from the material balance trend—well interference? (probably not).
TXL Unit Example: EURPI Map
EUR-Map — Contour Interval 25,000 STB
EURPI mimics OGIP—EURPI shows a "ridge" along the right-hand-side of the map. This is trend is consistent with the geologic description.
TXL Unit Example: OOIP Map
OOIP-Map — Contour Interval 400,000 STB
OOIP also shows the same trend along the right-hand-side of the map. The northeast corner has the very highest re-serves, west-southwest region has the lowest reserves.
TXL Unit Example: kh Map
kh-Map — Contour Interval 10 md-ft
kh mimics OOIP/EURPI—major issue is that reserves and kh are lowest in the west-southwest region—this discouraged the operator from infill drilling in this region.
TXL Unit Example: OOIP Comparison
This plot provides a comparison of the OOIP computed using well log analysis versus the OOIP computed from decline type curve analysis. Note that OOIPlog is always greater than OOIPWPA.
Summary:
The TXL (Clear Fork) Unit is a very large dol-stone reservoir of moderate to low reservoir flow capacity. The production analysesconfirm a "ridge" of higher flow capacity, with lower, more dispersed trends on the flanks of this ridge.
This study was conducted because the operator wantedto characterize the reservoir without bias of reservoir simulation. The production-based analyses and the analyses performed using well logs compare reasonably well, al-though significant differences do exist.
In particular, we note thatOOIPlog is always greater than OOIPWPA—though this could (rea-sonably) be accounted for by considering the basis of the well log-derived reserve estimates.
Reservoir Characterization — TXL Unit(West Texas) — Slide 1