ty le ca cuoc 188bet Application of geochemical technique to reduce allocation cost for commingled production wells from multiple reservoirs

Summary

This paper presents a new technique which has been developed to achieve production allocation at a reduced cost by ty le ca cuoc 188bet Vietnam Petroleum Institute (VPI). A case study of using geochemical fingerprint technology to back allocate commingled well stream from multiple reservoirs in an offshore basin, southeast Vietnam has been carried out. A large number of oil samples were collected over time and analysed by gas chromatography for their fingerprint and production allocation. Quantitative results were attained using a proprietary computer program which mathematically calculates ty le ca cuoc 188bet relative contributions of end member oils based on chromatographic data. ty le ca cuoc 188bet geochemical allocation results compare very favourably with ty le ca cuoc 188bet metering data. ty le ca cuoc 188bet success of ty le ca cuoc 188bet geochemical allocation allows ty le ca cuoc 188bet cost of field operation to be reduced and effective support to be given to ty le ca cuoc 188bet production management.

Key words: Back allocation, gas chromatography, geochemical finger-printing.

1.    Introduction

Crude oils originating from different producing zones, wells, or fields are mixed through commingling operation for reducing operation cost, improving production efficiency and field management. For technical reasons, it is sometimes necessary to quantitatively deconvolute these mixtures to facilitate monitoring of individual zones, wells, or fields. For example, where multiple pipelines commingle, an accurate assessment of individual field contributions may be essential for establishing sales value or tax liability because oil quality or tax rates can be different between neighbouring fields that share a transport pipeline to terminal facilities. ty le ca cuoc 188bet ability to back allocate helps in effectively managing reservoirs and production operations.

Normally, field/reservoir allocation is done by monitoring individual field production with flow meters  or by MPLT (Memory Production Logging Test) running. However,inthiscase,therewasalackofdedicatedmetering for production from some fields/reservoirs during a period of time. Moreover, ty le ca cuoc 188bet tax liability was different for those neighbouring fields that shared a pipeline to transport oil to terminal facilities. Thus, it was necessary to investigate alternative methods for reallocating production from these fields/reservoirs in order to determine an accurate field/reservoir contribution. ty le ca cuoc 188bet use of geochemical fingerprinting technique presented in this report is one method to re-assess and crosscheck individual field/ reservoir contribution to commingled pipeline oils.

Geochemical-based oil allocation has been applied for allocation of commingled production from multiple zones and production from multiple fields to a single stream [1, 2]. This method uses whole-oil chromatography distinctive peak height ratios to quantify ty le ca cuoc 188bet contribution of each individual production stream to a commingled production stream. ty le ca cuoc 188bet distinctive compounds are natural fingerprints for oil classification or oil grouping and used for proration of each end-member oil in ty le ca cuoc 188bet commingled oil [3].

2.    Methodology

ty le ca cuoc 188bet methods are based on ty le ca cuoc 188bet assumption that oils from separated reservoirs or different parts of a reservoir bear different chemical signatures or distinctive chemical fingerprints.  At  ty le ca cuoc 188bet  reservoir   scale,   steep   gradients   in  oil  composition  and   associated   fluid   properties   are understood to be ty le ca cuoc 188bet product of preferential biodegradation of different hydrocarbons, which gives  oils a distinct molecular signature or “fingerprint” related to ty le ca cuoc 188bet level of degradation. This natural variability in oil composition can be used to allocate oil production along horizontal wells or to assess ty le ca cuoc 188bet contribution of different production streams in commingled wells by mapping ty le ca cuoc 188bet original oil composition distribution.

Each oil type is  identified  and  clarified  through  a  data  set of physicochemical  properties  named  fingerprints.  Depending  on different targets, oil fingerprints are determined by gas chromatography, biomarker analysis, IR, UV-VIS instruments, trace element, and isotope analysis which can lead to high capacity of oil type identification. For example, ty le ca cuoc 188bet original oil type of gasoline and oil spill can be determined by fingerprint analysis.

Using whole oil gas chromatography fingerprints in order to identify oil type is ty le ca cuoc 188bet most popular method which uses a set of peak height ratios to identify oil type. ty le ca cuoc 188bet height or area of a GC (gas chromatography) peak reflects ty le ca cuoc 188bet concentration of a hydrocarbon component of ty le ca cuoc 188bet oil. Due to approximately 1000 peaks in a whole oil gas chromatogram, ty le ca cuoc 188bet distinctive peaks are usually chosen according to experience rather than their chemical nature. Therefore, many sets of GC fingerprints exist from different laboratories.

Depending on ty le ca cuoc 188bet oil field, these compositional differences exist for one or more of ty le ca cuoc 188bet following 3 reasons [4]:

-    Oils from different sources differ in composition since oils  from different source rocks have different times of generation and/or different migration paths.

-    Oil, which a source rock generates at a given time, differs slightly both from subsequently generated oil and previously generated oil due to continuous, subtle  changes  in  ty le ca cuoc 188bet maturity of source rock and changes in precisely which part of ty le ca cuoc 188bet source rock is in ty le ca cuoc 188bet oil window. Since no two compartments are of identical geometry, and since no two compartments have exactly ty le ca cuoc 188bet same filling history, it is difficult to achieve precisely ty le ca cuoc 188bet same homogenised composition in two separate compartments - even with oil from ty le ca cuoc 188bet same source.

-    Processes that affect oil composition after oil enters a reservoir (such as biodegradation, water washing, evaporative fractionation) do not operate to exactly ty le ca cuoc 188bet same extent in separate compartments.

Figure 1. A whole oil gas chromatogram [5]

Figure 2. Commingled production and allocation [6]

If two oil zones (1 and 2) were commingled, ty le ca cuoc 188bet respective contributions of ty le ca cuoc 188bet zones to ty le ca cuoc 188bet commingled sample could be determined by identifying ty le ca cuoc 188bet chemical differences between end-member oils, with ty le ca cuoc 188bet end member being pure samples from core or cuttings samples from ty le ca cuoc 188bet production well or nearby delineation wells to those of ty le ca cuoc 188bet produced oils (1 and 2). ty le ca cuoc 188bet combination of mass chromatograms as molecular fingerprint data and direct measurement of specific component abundances in oil samples are then made numerically. ty le ca cuoc 188bet data were then used to mathematically express ty le ca cuoc 188bet composition of ty le ca cuoc 188bet commingled oil in terms of contributions from respective end-member oils.

ty le ca cuoc 188bet relationship between a GC peak height ratio Y (measured in ty le ca cuoc 188bet GC of a commingled oil) and ty le ca cuoc 188bet GC peak height ratio X of ty le ca cuoc 188bet corresponding peaks in ty le ca cuoc 188bet “m” end- member oils being commingled is given by a linear relationship of ty le ca cuoc 188bet form:

In which:

Y = β1X1 + β2X2 + ... βmXm  (1)

Y: ty le ca cuoc 188bet peak height ratio matrix of commingled oil;

X1, X2... Xm: ty le ca cuoc 188bet peak height ratio matrix of m end-member oils;

β1, β2... βm: ty le ca cuoc 188bet percentages of m end- member oils.

Production allocation is ty le ca cuoc 188bet process of determining ty le ca cuoc 188bet values of β1, β2... βm for end-member oils.

In reality, there are multiple sources of error, including ty le ca cuoc 188bet following:

-    Analytical error in measuring ty le ca cuoc 188bet height of each GC peak;

-    Error associated with potential contamination of GC peaks;

-    Error associated with ty le ca cuoc 188bet non-ideality of ty le ca cuoc 188bet samples chosen as end-members.

Because of ty le ca cuoc 188bet various sources of error, certain GC peaks will do a better job than others at allocating each zone’s contributions to a commingled oil. It is impossible to know, in advance, which GC peaks will do ty le ca cuoc 188bet best job of ty le ca cuoc 188bet potentially hundreds available in an oil allocation process.

Figure 3. An example of NNMF (non-negative matrix factorisation) algorithm in least square technique [7]

ty le ca cuoc 188bet problem thus becomes one of a linear regression. Specifically, given a set of samples containing a value for each independent variable and ty le ca cuoc 188bet corresponding value of ty le ca cuoc 188bet dependent variable, ty le ca cuoc 188bet “β” values must be computed in a relationship of ty le ca cuoc 188bet form:

Y = β1X1 + β2X2 + ... βmXm + E

Where, “E” represents ty le ca cuoc 188bet error that is not captured by ty le ca cuoc 188bet linear relationship.

Linear regression can be used to converge upon a set of β value that minimises ty le ca cuoc 188bet sum of ty le ca cuoc 188bet square of errors (min|E|2).

ty le ca cuoc 188bet advantage of geochemical allocation

Geochemical allocation of commingled production from multiple zones in  a  single  well typically costs less than 5% as much as conventional e-line production logging. ty le ca cuoc 188bet cost saving is even more dramatic when compared to those for coiled-tubing-conveyed or tractor- conveyed MPLTs.

ty le ca cuoc 188bet low cost of geochemical production allocation allows field engineers to monitor output frequently over long time periods (e.g., weekly, monthly, and quarterly), allowing early identification of zone performance problems. ty le ca cuoc 188bet much higher cost of production logging limits that technique to infrequent use. Therefore, production logging typically provides only a snapshot of ty le ca cuoc 188bet production origin at ty le ca cuoc 188bet time ty le ca cuoc 188bet log was run, rather than a continuous performance history [2].

Geochemical fingerprinting techniques are applicable to highly deviated and horizontal wells, in addition to vertical wells. By contrast, production logging interpretation is problematic in highly deviated wells. Geochemical fingerprinting techniques can be applied to all types of pumping wells, including those with tubing-deployed electrical submersible pumps, and progressive cavity pumps. Other than  those with unusual completion style, such as Y-block completion, most pumping well cannot accommodate a production logging tool, because ty le ca cuoc 188bet pumping apparatus prevents logging tool’s access to ty le ca cuoc 188bet underlying perforated interval.

ty le ca cuoc 188bet geochemical allocation approach can also be used to assess ty le ca cuoc 188bet contribution of multiple fields to commingled pipeline production streams. There are some additional advantages including ty le ca cuoc 188bet ability to allocate in ty le ca cuoc 188bet absence of flow meter data, and ty le ca cuoc 188bet ability to identify problems with flow meter data.

Procedure

Oil samples collected from wellhead were taken to ty le ca cuoc 188bet laboratory for geochemical analysis. GC processing was carried out by Chemstation software, chemometric tools and  polynomial  statistic to group oils and identify distinctive pairs of peaks for allocation calculation.

3.    Case study of geochemical production allocation

Geochemical-based allocation method was developed by ty le ca cuoc 188bet Vietnam Petroleum Institute and has been applied for hundreds of oil samples collected from different fields. ty le ca cuoc 188bet paper introduces ty le ca cuoc 188bet application of this method for commingled well P01 in A field, offshore Vietnam.

Figure 4. ty le ca cuoc 188bet principal diagram of a GC-FID system [5]

Figure 5. Agilent 6890N gas chromatography

Table 1. Oil samples collected from A field

Sampling and analysis

Miocene reservoir, A field, includes 2 pay zones: clastic and carbonate. P01 well started producing in 2011 and has been perforated at both clastic and carbonate reservoirs. In order to determine ty le ca cuoc 188bet oil contribution of these two reservoirs to P01 well, clastic and carbonate oil samples from P02 and P03 respectively were collected to be ty le ca cuoc 188bet end-members.

ty le ca cuoc 188bet whole oil samples (Table 1) were fully analysed on Agilent 6890N. Gas chromatograms are input data for Geochemical Allocation software to identify oil group and allocate commingled production.

Qualitative results

Oil - oil correlation is usually evaluated according to [1, 8]:

-    light hydrocarbon distribution (based on C7 isomers);

-    hierarchical cluster analysis (based on whole oil gas chromatograms).

Light hydrocarbon distribution (B-F diagram) was used to determine ty le ca cuoc 188bet differences between Miocene oils produced from ty le ca cuoc 188bet clastic and carbonate reservoirs of Afield. Figure

6 shows ty le ca cuoc 188bet correlation between aromatic index (toluene/n-heptane, B) and saturated index   (n-heptane/methylcyclohexane,   F). ty le ca cuoc 188bet  differences  between  oils  produced   from two pay zones are displayed through alkane, aromatic and naphthene hydrocarbon correlation. ty le ca cuoc 188bet negative slope illustrates ty le ca cuoc 188bet secondary alternation such as evaporative fractionation, thermal cracking, water washing, and biodegradation [8]. When this slope translates to ty le ca cuoc 188bet right, ty le ca cuoc 188bet maturity of source rock generating these oils increases.

Figure 6. B-F diagram of wells P01, P02 and P03

Figure 7. Hierarchical cluster analysis diagram of VPI-P01, VPI-P02 and VPI-P03

As shown in ty le ca cuoc 188bet B-F diagram,  ty le ca cuoc 188bet  samples of VPI-P02 and VPI-P03  are  located at two separated areas, it means that ty le ca cuoc 188bet oil geochemical properties from these two wells are highly different (VPI-P02 represents oil from clastic reservoir and VPI-P03 represents oil from carbonate reservoir). Moreover, ty le ca cuoc 188bet oil samples from these VPI-P02 and VPI-P03 are located along two parallel straight lines which therefore can be considered as ty le ca cuoc 188bet trends of clastic and carbonate oils respectively.

ty le ca cuoc 188bet oil samples from VPI-P01 were found very near ty le ca cuoc 188bet location of carbonate trend. These results illustrate that oil from carbonate reservoir mostly contributes to ty le ca cuoc 188bet oil production stream of VPI-P01.

Using all GC whole oil data of VPI-P01, VPI-P02 and VPI-P03 as an input data to run ty le ca cuoc 188bet cluster analysis, ty le ca cuoc 188bet dendrogram is shown in Figure 7 with two distinct groups. Accordingly, ty le ca cuoc 188bet samples of VPI-P01 and VPI-P03 are grouped in one cluster and ty le ca cuoc 188bet other cluster is VPI-P02 with very large distance. Hence, ty le ca cuoc 188bet oils from VPI-P01 and VPI-P03 have a distinct carbonate reservoir signature, whereas ty le ca cuoc 188bet oil from VPI-P02 has clastic signature. ty le ca cuoc 188bet distances between ty le ca cuoc 188bet groups (along ty le ca cuoc 188bet x-axis) are a relative measure of ty le ca cuoc 188bet magnitude of differences among ty le ca cuoc 188bet oils. Therefore, carbonate and clastic oils are clearly separable with large compositional discrepancy. Once again, this result proves that ty le ca cuoc 188bet oil flow from carbonate reservoir mainly contributes to ty le ca cuoc 188bet production stream of VPI-P01.
In addition, from over 500 chromatographic peaks (corresponding to more than 500 hydrocarbon compounds in a GC chromatogram from C6 to C14), through ty le ca cuoc 188bet adaptive algorithm and visual inspection, 26 pairs of distinctive chemical compounds (or 26 distinctive peak height ratios) were screened and chosen to display on ty le ca cuoc 188bet stardiagram. According to ty le ca cuoc 188bet star diagram, ty le ca cuoc 188bet difference between ty le ca cuoc 188bet geochemical properties of VPI-P01/VPI-P03 and VPI-P02 can be easily observed (Figure 8).
 

Figure 8. Polar (star) plot of selected peak ratios for well P01, P02, and P03

Quantitative results

Assuming oil from well VPI-P02  is  an  end‐member  oil of ty le ca cuoc 188bet clastic reservoir and oil from well VPI-P03 is an end-member oil of carbonate reservoir, ty le ca cuoc 188bet oil from well VPI-P01 is now considered as commingled oil from two reservoirs and therefore need to be allocated. Distinctive peak height ratios are chosen from approximately 1,000 gas chromatography peaks from C6 to C35 as input data of ty le ca cuoc 188bet Geochemical Allocation Software for allocation calculation.

ty le ca cuoc 188bet allocation results of commingled well VPI-P01 show ty le ca cuoc 188bet contribution of both clastic and carbonate reservoirs to oil stream of P01 and vary from time to time. However, oil from carbonate reservoir mainly contributes tocommingled oil stream of well P01 during ty le ca cuoc 188bet observed period. It illustrates that oil produced from P01 is characterised  by  oil produced from carbonate reservoir. These results are consistent with ty le ca cuoc 188bet qualitative results in 3.2.

In order to evaluate ty le ca cuoc 188bet accuracy and validate ty le ca cuoc 188bet technique, ty le ca cuoc 188bet geochemical allocation results were compared with field production data based on MPLT running for well VPI-P01. Allocation of well VPI-P01 oils based on logging result compares very favourably with ty le ca cuoc 188bet geochemical result on ty le ca cuoc 188bet same date. ty le ca cuoc 188bet high agreement (in this case less than 1%) observed indicates ty le ca cuoc 188bet validity of ty le ca cuoc 188bet geochemical fingerprinting method.

4.    Conclusion

Geochemical fingerprinting technique with gas chromatography is a valuable method to accurately allocate commingled production stream and production pipeline. ty le ca cuoc 188bet results of allocation calculation of commingled wells based on their geochemical fingerprints are in excellent agreement (generally within 3%) with ty le ca cuoc 188bet actual production logging data. This method can be used to replace other methods (MPLT or metering) to determine ty le ca cuoc 188bet oil allocation from commingled wells/ pipelines more frequently because of their cost saving and high accuracy.

References

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2. R.L.Kaufman, H.Dashti, C.S.Kabir, J.M.Pederson, M.S.Moon,   R.Quttainah,   H.AI-Wael.    Characterizing   ty le ca cuoc 188bet Greater Burgan field: Use of geochemistry and oil fingerprinting. SPE Reservoir Evaluation and Engineering. 2002; 5(3): p. 190 - 196.

3.    Barry Bennett, Jennifer J.Adams, Stephen R.Larter. Oil fingerprinting for production allocation: Exploiting ty le ca cuoc 188bet natural variations in fluid properties encountered in heavy oil and oil sand reservoirs. Frontiers + Innovation. CSPG CSEG CWLS Convention. 2009: p. 157 - 160.

4.    Brooks A. Patterson and Mark A. Beeunas, Geochemical comparison of Rang Dong Field oils, Cuu Long basin, Vietnam. 2006.

5.    David K.Baskin, Alan S.Kornacki, Mark A.McCaffrey. Allocating ty le ca cuoc 188bet contribution of oil from Eagle Ford formation, ty le ca cuoc 188bet Buda formation, and ty le ca cuoc 188bet Austin Chalk to commingled production from wells in South Texas using geochemical fingerprinting technology. AAPG Annual Convention and Exhibition, Pittsburgh, Pennsylvania. 19 - 22 May, 2013.

6.    Scott Ramos, Brian Rohrback, Glenn Johnson, Russell Kaufman. Using gas chromatography and curve resolution to quantify contributions to mixed crude oils. 56th Pittsburgh Conference, Orlando, Florida. 2005.

7.    Daniel D.Lee, H.Sebastian Seung. Algorithms for non-negative matrix factorization. Advances in neural information processing systems 13. ty le ca cuoc 188bet MIT Press. 2001: p. 556 - 562.

8.    H.I.Halpern. Development and application of light- hydrocarbon based star diagrams. AAPG Bulletin. 1995; 79(6): p. 801 - 815.

9.    Marcio M.Lobão, Jari N.Cardoso, Marcio R.Mello, Paul W.Brooks, Claudio C.Lopes, Rosangela S.C.Lopes. Identificationofsourceofamarineoil-spillusinggeochemical and chemometric techniques. Marine Pollution Bulletin. 2010; 60(12): p. 2263 - 2274.

10.    Nguyen Xuan Thanh. Reservoir geochemical evaluation of ty le ca cuoc 188bet Rang Dong basement oils in offshore Vietnam. 1999.