Trial pitting, borehole drilling, and soil, sediment and groundwater sampling are important components of oil spill response and contaminated land assessment. These investigations provide detailed information on the subsurface geology and contaminant occurrence and transport but have disadvantages including worker safety hazards, cost and time required for completion, and may cause cross-contamination among aquifers. An alternative to such investigations applied in oil spill response is the Shoreline Cleanup Assessment Technique (SCAT) approach, which relies heavily on direct visual observations to assess the severity of oil contamination and guide cleanup efforts. Here, we compare SCAT observations of oil type, surface coverage and pit oiling with collected surface and subsurface sediment samples taken concurrently and analysed for a suite of hydrocarbon constituents. Results indicate that although limited sampling and analysis is required to chemically characterize the contamination, SCAT observations can be calibrated using limited sediment sampling and are sufficient to steer physical cleanup methods. This is particularly evident as even closely spaced chemical samples show high variability. A coarser direct visual observation is fit-for-purpose considering the wide variability in contaminant distribution at even local levels. In this contribution, we discuss the limitations of the different methods. Supplementary material: The modified SCAT data collection form, figures showing subsurface versus ground surface total petroleum hydrocarbons (TPH) and a variogram of TPH measured in the ground surface and subsurface samples, and data tables are available at https://doi.org/10.6084/m9.figshare.c.4534682 Thematic collection: This article is part of the Measurement and monitoring collection available at: https://www.lyellcollection.org/cc/measurement-and-monitoring
Several criteria and strategies have been developed to predict sand failures and to select appropriate sand control methods for improved completion designs and to maximise oil production at moderate unit technical cost. The depth criterion, SPADE equation, Rock Mechanic Equations incorporating Brinell Hardness Number and Unconfined Compressive Strength have been used extensively to predict sand production tendencies and to propose completion types. None of these criteria and strategies has explicitly incorporated the depositional environmental factor that defines the origin of these oil-bearing formations. A recent study aimed to correlate depo-belts and depositional environments to actual sand production using historical data of producing wells in the Niger Delta but covered only the Greater Ughelli depo-belt to some depths (SPE-163010). That study indicated a predominance of high sand producers in the channel sands depositional environment of the Greater Ughelli Depobelt. This paper therefore seeks to complete the investigation across all the remaining depo-belts and litho-facies and to share the review outcomes/ findings with the goal of establishing correlation between known rock mechanic principles and models used in sand failure prediction and sand control selection as a total system approach, providing wider solutions to sand control challenges in the oil industry.
Sand production in oil wells impairs full reservoir production capability, erodes sand face completions, down-hole tubular and surface equipment. The debilitating effects of sand production on surface production equipment are manifested in the plugging of flow lines, production manifolds and separators, leading to significant deferment in production due to downtime of facilities for sand clean out and component repair and replacement.2000 oil wells in the Niger Delta area have been reviewed to understand the sanding tendencies of the oil well completions and establish the completion strategy and practices that have successfully reduced sand production and its impact. It is observed that over 100 Mbopd oil is locked in as a result of produced sand. A plethora of sand control mechanisms such as Internal Gravel Packs, External Gravel Packs, Stand-Alone Screens, Premium Screens and Sand Consolidation Chemicals have been installed to reduce sand production in oil wells to acceptable rates but several cases of failures have been observed reviewing the past history of the oil wells.While several operators have developed guidelines to judge when sand control is required and how to operate the oil wells safely, there are still grey areas to be explored to understand the variation of formation consolidation indices from one Depo-Belt to another. The sand production performance of 2000 wells have been reviewed to examine whether the tendency for sanding can be attributed to oil well completion techniques or in-situ formation consolidation or a combination of both. It is also widely believed that formation burial depth can be used as a consolidation parameter to decide whether to include sand control in oil completion design or not.This paper seeks to share the results of the review of a large population of wells located and completed in different Depo-Belts in the Niger Delta with a view to helping operators streamline their decision-making process to include or not to include sand control systems in their oil wells for efficient production performance at less deferment due to sand production and lower completion and operating cost.
Early return on investment, high productivity indexes, late water/gas breakthrough and tight reservoir oil recovery are among the benefits of horizontal well over vertical well. Many operators have perfected and standardized the drilling and completion procedures of horizontal wells, however, the results of the different drain hole cleanup approaches have been inconsistent (especially where oil or pseudo-oil base mud were used during drain hole drilling). Conventionally, the removal of the damage caused by drilling mud filter cakes and filtrate is achieved with the aid of acid cleanup, Nitrogen lifting or brine wash. While the results of enzymes or acid cleanup in water based mud filter cakes removals are encouraging, the results in oil or pseudo-oil base filter cakes have been considerably inconsistent. This paper details the Pop-Off approach to the removal of drilling fluid damage and filter cake in horizontal wells with high heterogeneous permeability profiles. The paper described how the application of filter cake flow initiation pressure combined with treated drill-in fluid base fluid and reservoir's fluid solvent and dispersion power have delivered superior and consistent value on investment. The results from the application of this method showed remarkably low drawdowns and high productivity indexes. Field data resulting from this method demonstrates a history of 100% technical and economical success with more than 150% improvement in recovery and projected productivity index. In addition, there has been consistent improvement in sustenance of well productivity with wells treated with Pop-Off method over wells treated with previously applied conventional methods of filter cake removal. Introduction About twelve years ago, drilling horizontal wells was a new technology. Nowadays, horizontally placed wells are as popular as vertically placed wells. However, each well placement style has its benefits and areas of application. Horizontal well drilling and completion are continuously increasing because of its high flow area, high productivity index, longer water/gas breakthrough time, and suitability for tight reservoirs oil recovery and early return on investment. In the Niger-Delta most of the reservoirs are highly heterogeneous with high permeability. Consequently, the pay zone drilling mud is designed with wide range of particle sizes that filter and bridge rapidly with minimum filtrate penetration. The type of drilling fluids used in Niger-Delta has continuously been changing from Water base or polymer base to Oil and Pseudo-Oil base mud. Whilst water based mud is cheap, economical and has good rheological properties, its inability to effectively control highly reactive shale in Niger-Delta reservoirs has lead to increasing usage of Pseudo-Oil based mud. Despite the high cost of sales, high environmental impact, non compatibility with cements and low to medium impairment disadvantages of oil or pseudo oil based drill mud, it is preferred to water based drilling mud due to its high shale inhibition, high lubricity, controllable rheology and most of all their low fluid loss, thin filter cake and generally better return permeability. Calcium Carbonates and Barite are commonly used as weighting agent or as particulate for filter cake formation. Conventionally, the removal of the damage caused by drilling mud filter cakes and filtrate are achieved with the aid of acid cleanup, Nitrogen lifting or brine wash. While the results of enzymes or acid cleanup in water based mud filter cakes removals are encouraging, the results in oil or pseudo-oil base filter cakes have been considerably inconsistent. The poor performance of these various clean-up approaches in Oil phase is mainly attributed to downhole emulsion formation between oil and water phases, incompatibility between treatment fluids, drilling mud and in some cases formation of damaging byproducts. Wettability change and pronounced water block problems may also arise in low permeability zones. In order to eliminate the above listed problems, Pop-Off, an approach to clean horizontal hole was introduced and successfully applied. The approach has given consistent and rewarding results.
Urbanisation effects around fields in the Niger Delta has made onshore hydrocarbon production activities not to thrive in a clime of increasingly health, safety and environment (HSE) oriented operations leaving most well locations encroached by emerging towns, with flowline right-of-way (RoW) already encumbered. Sigma field is one of SPDC fields in the Niger Delta that were impacted by third-party encroachment. An initial assessment showed 26 producing oil conduits and 11 RoWs were impacted resulting into production deferment of ca. 10,300 bopd. Given an encroachment resolution cost of ca. US$37mln budgetary provision there was the need to carry out cost-benefit analysis of the additional investment. This paper presents the approach adopted to get the most out of the field in the Niger Delta whilst countering the effects of third-party encroachment through set criteria: well cluster based on common location, and creaming based on recoverable volume, conduit level reserves and conduit potentials. 19 conduits were recommended for re-opening with a life cycle recoverable volume of 33MMBOE saving US$9.6mln. It was concluded from preliminary economics that the encroachment resolution cost of US$37mln can be accommodated by the additional oil and gas production notwithstanding the rigour required for handling third-party issues.
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