Oil Based Mud Filtrate Effect on Downhole Samples Obtained for Crude Assay Testing. Magdy Samir Principal reservoir Engineer Aberdeen

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1 Oil Based Mud Filtrate Effect on Downhole Samples Obtained for Crude Assay Testing Magdy Samir Principal reservoir Engineer Aberdeen

2 Oil Base Mud Contamination when Sampling in Openhole

3 How do we correct for contamination? (SPE 56747)

4 OBM Chromatograms

5 Effect of Contamination on Saturation Pressure

6 Effect of Contamination on Single Phase Density

7 Saturation Pressure against Contamination Level

8 Variation of Liquid Fraction against Pressure

9 Variation of Single phase Viscosity with contamination

10 Effect of contamination on Asphaltene onset pressure

11 Crude Assay Testing Crude oil assay is the extensive detailed analysis of crude oil in the lab for refiners, oil traders and producers Each crude oil type has unique molecular and chemical characteristics. Assay data help refineries determine if a crude oil feedstock is compatible for a particular petroleum refinery or if the crude oil could cause yield, quality, production, environmental and other problems. The assay could be an inspection assay or comprehensive assay. Oil companies published extensive properties of their crude assays online

12 Crude Assay Analysis Physically distilling a crude or condensate in the same way that a refinery does to produce naphtha, gas oil, fuel oil and other fractions. The lab calculates potential yields for any given crude oil or condensate. The fraction is then analysed in the laboratory to give a client an accurate predication of the quality that the refiner / trader is likely to obtain should the purchase and refine the crude or condensate being assayed. Total Boiling Point (TBP) Distillation unit for crude oils and condensates apparatus Oil companies publish extensive properties of their crude assays online

13 Example of the summary page

14 The Challenges faced when trying to obtain crude assay samples on wireline in openhole Large volume of samples required (~ 11 gallon) And hence weight and length of the tools (high strength cable, Capstan unit) Contamination levels which are normally accepted for standard PVT analysis for oil are considered too high for crude assay analysis Very low contamination or zero contamination with OBM filtrate required

15 Focused Sampling Standard sampling. - One pump. - One sampling line. - Kv/Kh and Filtrate mobility enable contamination. - Longer cleanup, limited contamination level. Focused Sampling Concept. - Step change on sampling technologies. - Sampling using two synchronized pumps. - Split/independent flow lines for both pumps. - Optimize guard and Sampling line rates ratio. - Proven reduction in clean-up times. - Lowest contamination levels (even 0% Achieved!!!).

16 Case Study Oil zone, 11 gallon of very clean crude oil sample required for assay analysis Focussed sampling equipped with large sample chamber planned (2 runs), and high tension deployment system 4 x 2 ¾ gallon sample chambers divided on two wireline runs Full well testing kept as a contingency Onsite GC analysis (PVTExpress) available on to confirm the quality of the samples Samples obtained and verified saving operators several days of rig time and additional costs

17 Conclusions OBM filtrate contamination has a huge effect on the hydrocarbon fluid being sampled. Analysis required and hydrocarbon fluid type and OBM filtrate composition need to be considered carefully during the job planning phase Standard sampling is not adequate for crude assay analysis. Focussed sampling is required Crude assay samples can be obtained on wireline provided that proper job planning and executions that will ensure clean and large volume samples are obtained and verified

18 Quicksilver Probe Examples Objective: low contamination sample Guard pump started MRPQ sample = Considerably Lower contamination * Pending Lab results

19 Thanks Questions...