Pioneer Natural Resources TRANSCENDING CONVENTIONAL LOG INTERPRETATION- A MORE EFFECTIVE APPROACH FOR SPRABERRY RESERVOIR Pioneer Natural Resources DICMAN ALFRED M.S Texas A&M University

LOCATION

HIGH’S AND LOW’S At least 15% of all oil remaining in class 3 (slope-basin and clastic basin) reservoirs may be in the Spraberry trend Estimated 6 billion bbl oil remain in Spraberry reservoirs Waterflooding was initiated in 1950’s without much success Current ultimate recovery is no greater than 10% of original oil in place Presence of fractures has a dominating influence on performance

OBJECTIVES To analyze logs effectively and determine average water saturation To establish pay zones and cut-offs To recommend a suitable logging program

CHALLENGES Absence of clean water bearing zones Fractured Nature of the Formation Lack of Rw value to establish water saturations using the models available in the industry Models Archie Simandaux Dual water Waxman-Smits Indonesian

SPRABERRY MAKEUP- LOOKS COMPLICATED ??

1U PAYZONE MINERALIZED FRACTURE

METHODOLGY DATA GATHERING DATA EDITING LITHOLOGY DETERMINATION CORE ANALYSIS LITHOLOGY DETERMINATION SOFTWARE PRIZM® DETERMINATION OF POROSITY EXPONENT m

P ½ CALCULATION AND PLOT DETERMINATION OF P ½ MEAN DETERMINATION OF WATER SATURATION RECOMMEND LOGGING PROGRAM

Why is matrix density is so vital for the analysis of fractured zones ?? Density porosity is given by By convention SANDSTONE 2.65 GM/CC LIMESTONE 2.71 GM/CC DOLOMITE 2.87 GM/CC

True matrix density can be determined INGREDIENTS FOR SUCCESS True matrix density can be determined From core analysis From complex mineral lithology plots (using software packages) By interplay between Hingle and Pickett plot (which also gives the cementation component “m”)

Determination of matrix density from core

4 MINERAL PLOT USING PRIZM® Shale streak marker

LITHOLOGY 1U WELL#37 The points fall in the sandstone region

HINGLE AND PICKETT INTERPLAY Assume “m” Find ρma Hingle Pickett m Log(ρma-ρb) (1/R t) (1/m) ρma ρb Log(R t) Estimate “m” Estimate “m” Hingle Pickett Find ρma (1/R t) (1/m) m Log(ρma-ρb) ρma ρb Log(R t)

Hey!!! That’s a fractured formation—Why?? m = 1.2 (m-b) ,GM/CC Rt , OHMM Hey!!! That’s a fractured formation—Why?? m = 1.2

COMPARISON IN WELL # 39 5U Sonic  Core  Core  Effective  Density  Density 

AVERAGE WATER SATURATION Calculated using a statistical parameter P ½, originally introduced by Porter, Pickett and Whitman. Empirically, P ½ has a normal distribution for intervals which are filled with water. Intervals with some hydrocarbon saturation deviate from the normal distribution. The parameter is defined by If Sonic Log is used,

Hydrocarbon zones Non-productive zones

P ½ mean

Hydrocarbon zones Non-productive zones

DETERMINATION OFAVERAGE WATER SATURATION Resistivity Index Conventional Water saturation is given by

WELL # 39 1U Sw BVW OIL

5U

Comparison of Core vs Porosity 1U Well#37 Effective  Density 

Non productive Zones P 1/2 mean Cummulative frequency

1U Density caliper lost contact 5U

WELL #37 Sw 1U BVW OIL

5U

CONCLUSIONS The Density log derived porosity is found to approximately correlate with core porosity after suitable corrections. The water saturation derived from statistical parameter P ½ gives acceptable values compared to the other models used in the industry . Sonic log gave better results than density log. This method can be employed in formations whose Rw is difficult to obtain. The payzones and cutoffs can be established from the saturation values

RECOMMENDATIONS An ideal Logging Suite for the Spraberry Trend will be Spectral Gamma log Density log Sonic log Induction log