SPE WVPS-613

Best practices in damage removal techniques for horizontal wells in Orinoco Oil Belt

D. Ávila, PDVSA; L. Lara, SPE, PDVSA; V González, PDVSA.

This paper was prepared for presentation at the 2015 SPE WVPS 3er South American Oil and Gas Congress held in Maracaibo, Zulia State, Venezuela, 27–30 October 2015.

This paper was selected for presentation by the SPE Western Venezuelan Petroleum Section Program Committee, following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the SPE Western Venezuelan Petroleum Section Program Committee and are subject to correction by the author(s). The material does not necessarily reflect any position of SPE Western Venezuelan Petroleum Section, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without written consent of the SPE Western Venezuelan Petroleum Section is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 350 words; illustrations may not be copied.

Abstract

The Orinoco Oil Belt (OOB) as a principal oil reservoir in the world mark a milestone in new technologies and innovation, this situation let us affront all inherent challenges and improve the productivity in this important zone.

The study was designed to asset increase in the production levels for horizontal wells, this specific type of wells represents most important support of production in Petro San Félix company operations. However, they are suffering an important reduction of production for natural declining factors and damage at liner face or welldown area.

The methodology was based on a selection of better candidates under technical and economic considerations, these opportunities were included in the evaluation matrix, measured, and compared to rank best options to work. In each case, geological properties and dynamics flow in the well were determined in the kind of treatment to use. The methodology has been reviewed with statistical results in order to include this feedback and improve it with the state of art.

Results for this procedure include 80 candidates wells basket. After 7 months activities, have been worked 38 wells and production increase of 1812 barrels per day.

Methodology could be used as model in other áreas around Orinoco Oil Belt because the applicability and economics was demostrate in the Petro San Félix simply used for this study.

Introduction

Zuata Principal Field has been operating since 1997 and all wells located in this area are supported for artificial lifts.

methods (PCP and ESP commonly). The reservoir pressure behavior is affected by natural decline, and this situation increase proportionally with each year of operating life in the well.

Commonly methods for recover originals production levels are focused on wellbore damage removal, these problems are typical for mature wells with sand, paraffin, or heavy oil production, due to this kind of materials a film is made over the production slotted liners keeping down hydrocarbon flow and reducing production potential in oils wells.

In this work all our efforts were focused to study the methodology and cut off points to assure profitability and technical viability of cleaning treatments, always looking for find better work strategies based in “self-learning” and “state of the art” philosophy.

We studied issues such as: Pre-cleaning treatment for production liner with solvents by jetting techniques, different kind of stimulation system on different kind of economical sceneries of stimulation in order to analyze better options in each case.

Field Description

The Zuata Field is located south of Anzoategui and Monagas states and has an extension of 300 Km².

More specifically SDZ 2XA1 reservoir is our interest area. The OOIP contained is 21.8 billion barrels, and remaining oil reserves are around 3.8 billion barrels.

The principal production zone is the formation Oficina of age Inferior Miocene.

In the fig. 1 is possible show the sequence distribution of productive sands and the electricasl responses for prospectivity.

Figure 1. Stratigraphic column of Zuata Principal field.

Stimulation Techniques

There are serveral stimulation practices actually, but not all are applicable for unconsolidated sands.

Figure 2. Damage removal techniques

Considering the information showed in the fig. 2, only chemical and mechanical stimulation could be considered for unconventional reservoirs of the Orinoco Oil Belt, due effect of frack procedures in not relevant for unconsolidated sands.

For Zuata Principal Failure analysis is necessary show information in the fig.3, because situations as drilling/completions problems can be identified reviewing the drilling summary of each well. In case of problems caused by geological or production situations must be studied from this information. However, the typical behavior in the candidate wells is a good initial production and after a few years presents considerable down production.

In this phase, research of well information will be the key for an analysis accurate and the time used for it will be dependant of the quality of the information collected.

Figure 3. Cause – root scheme for formation damage failure mode in horizontal wells

In Zuata Field candidates, were reviewed since his drilling start to last information for production history and the mostly of them did not present considerable operational problems during drilling or completions operations.

Geological considerations were discarded because did not find elements indicated of problems with clays or sand migration.

Blocks for emulsion or water will not be considered because the historic of analysis of fluids did not show important quantities of emulsion.

Methodology

The key stage for this work was the candidate selection. In order to get the best results was applied the following premises.

Multilateral wells were excluded; due to mechanical complexity could be a problem for cleaning operations. Presence of sand in the window zone for multilateral wells

with level 3 completions is common in this area and this kind of obstruction could represent a delay for all intervention operations.

Analyzing the production history for candidate wells, was possible to exclude those with high production of water or gas, because this is a signal of intrusion of non-desirable fluids.

Another cut-off parameter considered was the cumulated oil production and remaining reserves.

For single wells was collected information as: production history, PCP replacement history, failure history, fluids analysis history and other relevant information.

Geological information was reviewed and organized by the same form. Parameters as thickness, porosity, permeability, horizontal section drilled, and water saturation were collected and analyzed in databases for statistical interpretations of successful sceneries.

Through a commercial software we got declining tendencies for all candidate wells, in this stage, was very important determine “abnormal decline” in the well, due it suggest that a problem could be causative of the production decreasing.

Also, another objective in this process was to search for abnormal behaviors in the well, represented for fall out of PIP, down submergence, stops in well operation and other relevant situations that represent a symptom of mal function in the well.

After collect all information about possible candidates, we built a main database with all pre – cleaning conditions for each well. This tool will be important for future comparations of statistical behavior for worked wells.

In the Fig. 4 is shown a flow diagram with the methodology process used for candidate selection.

Figure 4. Methodology for candidate selection.

The stimulation process was realized for a small rig with capacity to pull out the well completion, after that a cleaning BHA was introduced for check the sand presence, in case of find sand, will be necessary a first cleaning travel. If the well is clean, procedure indicates to push down the BHA at the end for pump the diesel in all the horizontal section.

Finally, with first 7 months results our study shows a review and interpretation of this results and the impact over production and economics factors.

Results.

As is shown in the fig. 5, the profitability behavior is dependent of the time used for the work and the amount of barrels increased after the cleaning.

In this case, each day used for cleaning work represent a lost of production in active wells, because normally the best candidates are wells with a reduction in the potential production

Figure 5. Comparative chart of profitability.

Analyzing fig. 5, cleaning works are only profitable if the work time does not exceed 10 days and result gives an increase of production over 50 B/D. In the figure, the blue zone is a negative result representation.

Figure 6. Graphic of success distribution by profitability.

Considering the cut off parameters for profitability, is possible filtering in the fig.6 of only wells over 50 B/D in order to consider “the successful work” and refine the statistical information.

For a total of 38 wells cleaned with solvent, only 14 resulted less than 50 B/D as is represented in fig. 6. This 63% of wells with a positive increase of production has allowed reduce the decline levels in the field in a 50% for 4 months.

Figure 7. General graph of success distribution.

In order to determine the most important influencing parameter in the success of the work, it was performed statistical reviews with the information of the successful wells. The studied parameters were thickness, horizontal section length, porosity, permeability, sequence of sand, water saturation and initial potential production

After statistical review, only the behavior of the sequence of sand gives representative information about a success tendence.

The fig. 8 shows as the inferior sequence of sands in the stratigraphic column return the best results after cleaning. This result coincide with the initial candidate selection due this sands represent the most important and massive packages with better properties than the superior sequences.

Figure 8. Graph of success distribution by sequence of sand.

The importances of find the state of the art in this kind of activities, reside in the necessity of improve the oil well behavior during the “productive life”. This stage could be result in a premature failure if the drilling/completion operations were not accomplished appropriately.

The economic factors play an important role in the decision matrix, and benefits related with less cost and time of work for

the same increase of production generally influence the investments. In this case, fig. 9. Shows as cleaning procedure is an excellent option if is compared with other methods as EHD or RA/RC.

Figure 9. Comparative figure of cost and benefits with other procedures.

Conclusions

1. The oil well history is decisive to obtain the right treatment since drilling.

2. The profitability for works of damage removal is representative only for wells over 50 barrels of production increase.

3. The 63% of wells cleaned resulted with an increase of production over 50 barrels per day.

4. More than 75% of wells drilled in lower sands and cleaned, got an increase in their production over 50 BOPD.

Acnowledgements

We are thankful to PDVSA Petro San Félix for support and give us permission to publish the results of this work.

References

1. G. Paccalonni; M. Tambini; M.Galoppini. “Key Factors for Enhaced Results of Matrix Stimulations Treatents” SPE 17154, presented at SPE Formation damage control symposium 1988.

2. M. Economides; K.B. Naceur; R.C. Klem. “Matrix Stimulation Meethods for Horizontal Wells”. JPT. 1991.

3. M.L. Ventresca. “Definiciones generales de daños a a formación y estimulaciones de pozos” PDVSA Intevep. Short Course.

Nomenclature

OOB: Orinoco Oil Belt.

PCP: Progressive Cavity Pump. ESP: Electro Sumersible Pump. PIP: Pressure Intake of the Pump. BHA: Bore Hole Assembly.