This paper was also presented as SPE 100948 at the 2006 SPE International Oil & Gas Conference and Exhibition in China held in Beijing, 5–7 December 2006. Abstract Sand production is a major concern for many operators. It can impact production, cause erosion in downhole and surface facilities, require additional separation and disposal, and lead to significant economic loss. On the other hand, precautionary but unnecessary sand prevention will mean unwarranted reduction in productivity. Reliable sanding prediction analysis thus provides a basis for designs that achieve appropriate sand management strategies and maximization of economic production, and overestimates or underestimates of sanding risk increase the chances of serious economical loss. This raises the question of how accurate and reliable sanding predictions might be achieved without overcomplicating the analyses and without requiring complex lab and field data that, in most instances, will be unavailable or the acquisition of which will incur unwanted delays and costs. This paper presents the case of a sanding study for the Messla field in Libya; a field that has produced oil for more than 30 years. This field experiences massive sanding from some wells but experiences no problems with other wells. This variation made the Messla field an ideal candidate for a detailed sanding and geomechanics investigation aimed at optimizing completions and production and at dramatically reducing the current sanding without having to enter into a lengthy data acquisition programme or time-consuming modelling. In this study, sanding prediction analyses were conducted using a technique that combines easily measurable lab data, log data, and analytical calculations with empirical methods that are supported by the results from previously run rigorous and advanced numerical code. The result of this integration is a sanding analyses tool that uses input parameters such as rock strength, geostresses, and particle size to:account for plasticity effects that modify the strength behaviour of sands surrounding openhole wells and perforations during drawdown to reduce uncertainty and conservatism such as seen in simple elastic models,account for scale effects associated with different perforation and borehole diameters,provide a significant improvement and predictive capability over simple empirical methods,provide the above accuracies without needing complex or extensive lab programmes to determine advanced rock mechanics properties. The application of this approach to the Messla field and a later comparison of the results to actual field data and observations validated the analyses and methods used. The application and comparison also disclosed that the approach was not only able to provide results that closely matched field experience but was also able to predict correctly, to the year, the onset of sanding in wells. This paper describes the methods employed in this investigation, provides details of the data acquisition and processing required, and demonstrates that accurate sanding predictions can be achieved by focusing effort on certain input data, targeting and reducing specific uncertainties, and by employing pragmatic models that do not rely on over-complicated measurements and analyses. Introduction The giant Messla field is located in the southeast portion of Sirte Basin in Libya, approximately 500 km southeast from Benghazi (see Figure 1). The field, operated by AGOCO, has been producing for over 30 years, and since the mid-1980s some wells have suffered massive sanding while others have not. 1 A geomechanics and sanding study was initiated in 2005 to investigate the reason for this variation, to evaluate the severity of sanding risk in other wells, and to provide the information and interpretations needed to design appropriate completions, maximize economical production and optimize future reservoir management.
Innovative ideas and improvements to existing technologies are extending the ability to develop prospects in shallow waters from onshore drilling locations following the world's first two successful shunttube, uphill gravel packs in fishhook wells. Drilled from surface locations on land in Brunei with subsea locations offshore, these uphill gravel pack completions, incorporating shunt-tube technology, improve recovery and extend the fishhook completion technique to wells with critical well trajectories. SERIA FIELDAfter more than 80 years of production, Seria field, extending 25 km along the coast of Brunei, is still yielding new oil discoveries, with more than 900 wells drilled and cumulative oil production exceeding 1.1 billion bbl. In 2004, new oil was discovered just under the shallow marine surf zone on the northern flank, called the Seria North Flank (SNF) area. These marginal targets are uneconomical when drilled from offshore, so drilling and completion was conducted from onshore beach locations using fishhook (FH) well technologies to allow commercial exploitation.Since 2007, more than 50 FH wells have been drilled. Wells with inclinations less than 120° have been gravel packed using the reverse port gravel packing (RPGP) technique, a special tool setup that allows slurry to be pumped from the toe of the completion for gravel placement from the toe to the heel of the open hole. DEPO WELL DEVELOPMENTWith the successful completion of the SNF wells, the Darat Early Production Opportunity (DEPO) Phase 1 kicked off in early 2009. Other offshore targets that hug the Seria coastline were identified and developed in August 2010, using existing onshore infrastructure for early production.The focus of DEPO is the blocks in the offshore Anduki area shown in Fig. 1, as Cluster B and Cluster C, targeting 14 individual blocks. In the DEPO prospects, well targets became more challenging, pushing the well inclination up to 141°, with longer openhole intervals and some with shallow true vertical depth (TVD) of about 400 m, to optimally develop the field. All the SNF wells were drilled at well deviations less than 119°, and the RPGP technique was successfully applied in wells up to 115° of inclination.The DEPO project was projected to add early production from the mature Seria oil field. The thin sand-shale stacked reservoir accumulations are in fault-dip closures, near shore in water depths of 5 m or less, and are accessible from a land beach location. Successfully completed wells are tied into existing infrastructure for immediate production.The DEPO wells required longer openhole intervals. At least seven wells required deviation angles greater than 120°, which posed a technical challenge of ensuring 100% annular pack of the pre-completion. Past experience in gravel packing intervals in the 50°-60° deviation range in various fields in Brunei demonstrated a low success rate in achieving a full pack using the standard completion techniques.Four of the wells in Phase 1 were selected for evaluation of openhole gravel pack ...
Sand production from the Sarir field became a major concern for AGOCO at the end of the 1980s when ESPs were introduced to the field. The sanding severely impaired the performance of field, and consequently led to significant economic loss.AGOCO recognized that it was facing a major challenge in terms of understanding potential sanding risk for Sarir, and that it was necessary to design and implement a sandface completion and sand management strategy for more than 400 wells in the field. It was decided to apply a particular systematical approach, termed as Sand Management Solution (SMS), to properly address the sanding issues it was facing, which involved prediction, prevention, monitoring, and, if required, remediation activities. The first step in the SMS was to obtain a clear understanding of the cause and the mechanism for the sand production. This knowledge was required because attempts to run new completion designs without knowing the cause of the sand and understanding the risks had been proved costly, and would be likely to fail.To this end, a SMS was implemented in Sarir field. The work started from geomechanical reservoir characterization including geomechanics core laboratory test and mechanical earth model building, sanding prediction and evaluation, and a detailed review of sanding history to understand the severity of the sanding risk and sanding mechanism. Based on this knowledge, sanding management and remedial completion measures were devised that would minimize economic loss caused by sanding and optimize hydrocarbon production.This paper provides details of implementation of this SMS in the Sarir field, and demonstrates that a systematical approach is required when addressing sanding issues in giant mature fields such as Sarir.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper described a case study involved an investigation in a field in Libya, where massive unexplained fill had been reported accompanying obstruction of production for majority of production wells since the onset of production, indicating possible sanding issues for this field.To investigate this problem, relevant data from different sources and different domains (i.e., wireline logs, laboratory test data, drilling data, well data and field data) were integrated to generate a Mechanical Earth Model (MEM). This model provided the descriptions of the rock strengths and insitu stresses in the reservoir formation. Somewhat surprisingly, the model, backed up by the core laboratory test data, observations from core inspection and thin section analyses, revealed the rocks to be extremely hard and strong, and therefore highly unlikely to sand. These findings contradicted with initial impression and previous expectation on this sandstone that it should have been sand-prone formation. Facing these apparent inconsistencies, the investigation moved beyond an initial focus of sanding risk evaluation and sandface completion optimization. The final results revealed that the problems facing the field were other than conventional sanding and formation failure, and that they involved some rather interesting and misleading phenomena, such as precipitation of salt from production, tubing scale, spalling of borehole wall with drawdown and cavings bridge (cavings might fall into and become wedged in the openhole, forming a bridge with no material beneath).The investigation concluded that installing sand control facilities were unnecessary, which otherwise would have cost millions of dollars without correctly addressing the real problem that this field was facing. The study highlighted the importance of a thorough investigation of the mechanism and source of sanding rather than premature conclusions based initial, and potentially misleading evidence. It also highlighted how the integration of information from different sources and disciplines were able to correctly identify and address a particular borehole fill problem, allowing for optimizing field operations, field management and workover strategies.
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