Drilling Success Research Articles

Techbits: China Workshop Examines Fractured Carbonate Reservoirs

Techbits An SPE Applied Technology Workshop (ATW) on “The Characterization of Effective and Efficient Development of Fractured Carbonate Reservoirs” was held 15-18 June 2014 in Nanjing, China. Participants reviewed recent advances in exploration and production and the technical challenges presented by these reservoirs. A variety of carbonate reservoirs exist worldwide, mainly paleokarst reservoirs. Because of various scales, poor continuity, strong heterogeneity, accumulation in vugs and fractures, and complex flow behaviors, the efficient development of fractured carbonate reservoirs is quite challenging. Li Yang, cochairperson of the workshop, opened the session and ATW Chairman Wang Zhigang delivered one of two keynote speeches. He focused on the challenges and current activities of a key carbonate reservoir, Tahe, that he said represented the theme of the ATW. Usman Ahmed, also a workshop cochairperson, introduced the second keynote speaker, Christine Ehlig-Economides. She recalled an ATW a decade ago that also had focused on the Tahe reservoir. She set the stage for a discussion on how much the industry has advanced and the challenges that lie ahead. In his keynote speech, Wang of Sinopec described the technical challenges and techniques used at Sinopec’s Tahe oil field in western China. The Tarim basin is the company’s largest carbonate play, with proven reserves of 1.3 billion tons and depths of 5300 m to 6300 m. The oil and gas accumulated in pores, vugs, and fractures of severe heterogeneity and depth make it difficult to predict and describe reservoir characteristics, he said. Carbonate reservoir characterization and evaluation techniques have been developed that have improved the predictability of the carbonate reservoir and its distribution and have increased drilling success, he said. In the Ordovician carbonate reservoir of Tahe, a series of techniques such as paleokarst landform categorization, paleokarst cycle division, hydrocarbon accumulation period analysis, logging for reservoir identification, and evaluation have been implemented. In addition, massive acid fracturing (high pumping pressure, high injection rate, large scale) has become a major technique for development at the field. In sum, the technical challenges are: Ultradeep, highly heterogeneous reservoirs with low-resolution seismic data make it difficult for reservoir prediction. The form of fractures and vugs and oil and gas accumulation in such reservoirs make reservoir modeling difficult. A variety of reservoir fluid systems exist, which lead to a complex oil-water distribution. Current simulation techniques need to be further improved. Severe channeling and breakthrough were detected after waterflooding was applied. Further research is needed to improve waterflooding, residual oil characterization, and water-control techniques. Drilling activities are extremely challenging and costly. Drilling technology needs to be further developed or modified.

Predictors of success of laparoscopic ovarian drilling in women with polycystic ovary syndrome: an evidence-based approach.

Laparoscopic ovarian drilling (LOD) is currently recommended as a successful second-line treatment for ovulation induction in women with clomiphene citrate (CC)-resistant polycystic ovary syndrome (PCOS). To provide a comprehensive review of the current evidence regarding different clinical, biochemical and ultrasonographic parameters that help in predicting ovulation and or pregnancy after LOD. A PubMed search of published studies on LOD and reproductive outcome was conducted using defined keywords. Abstracts of 121 articles were screened and relevant articles were identified. Clinical studies were included with priority for level I evidence, i.e., randomized controlled trials (RCTs) followed by other levels. Based on the current evidence, LOD could be predicted to result in poor reproductive outcome in women with CC-resistant PCOS when they are obese (BMI>25kg/m(2)), long duration of infertility>3years, low basal LH levels<10IU/L, marked biochemical hyperandrogenism (testosterone levels≥4.5nmol/L, free androgen index>15) and high basal AMH≥7.7ng/mL. Setting eligibility criteria based on the existing evidence concerning predictors of success of LOD is critical not only for improving its outcome, but also to avoid unnecessary surgery with possible risk of impairment of ovarian reserve and other complications.

Rheological Characterization of Shale – Mud Interactions

In a bid to identify a best drilling fluid for a problematic oil field in the Niger Delta region, rheological tests were carried out on three mud samples; BW 1 , BW 3 and BW 4 . The results affirm that the load bearing capacity of XP-07 formulated as BW 3 and BW 4 in this investigation is excellent and fall within the same range or even better than those of REF Mud with a more than 90% drilling success history in Niger Delta. The rheological changes of XP-07 with increase in temperature and “assimilated” microscopic shale particles are very negligible and smaller than those of REF mud. XP-07 has been strongly recommended for all drilling operations in the problematic field. It has been re-emphasised as part of our recommendations that new guidelines for the close monitoring of drilling fluids supplied by mud companies and those actually used in the field (during drilling) be put in place. Key words: Shale – mud interactions; Rheological characterization; Niger delta

‘Too soon’ to confirm success of Antarctic lake drilling

‘Too soon’ to confirm success of Antarctic lake drilling

Mapping deeply-buried geothermal faults using microtremor array analysis

SUMMARY In this paper, the spatial autocorrelation microtremor array analysis is utilized to map deeply-buried subtle faults that have primary controls on geothermal reservoirs. We identified a low-velocity anomaly which is approximately 50 m wide at about 550–1400 m deep. A well drilled based on this anomaly later successfully produced hot water and further proved that the low-velocity anomaly was caused by a highly fractured zone at depths from 700 to 1500 m. Our results clearly demonstrate that the microtremor survey method can be effectively utilized to map deeply-buried faults and structures for geothermal energy exploration. The most effective way to increase the drilling success rate and, hence reduce the geothermal exploration risk, seems to be the development of new exploration methods and the integration of various geophysical technologies.

Swelling Characteristics of Shales and Their Dispersion in Drilling Muds III

This is a report of a critical analyses of XP-07 Niger Delta shale interaction studies under both ambient and high-temperature/pressure conditions. The results affirm the following: 1. XP-07 is thermally very resistant and easily amendable to formulation adjustments to cope with even highly reactive shale problems. 2. The viscosities and filtration properties are perfect and considerably constant. 3. The effect of shale on its rheology is very minimal even at high temperatures. 4. Thhe load-bearing capacity of XP-07 formulated as BW3 and BW4 in this investigation is excellent and falls within the same range or even better than those of reference mud with a more than 90% drilling success history in the Niger Delta. 5. The rheological changes of XP-07 with increase in temperature and assimilated microscopic shale particles are negligible and smaller than those of REF mud. 6. XP-07 has been strongly recommended for all the oil-producing company drilling operations, particularly in the problematic oilfields such as Tun and Opuks. 7. XP-07 is recommended exclusively for use in all Eastern Area projects because of possible occurrences of massive bodies of swelling shales in the offshore regions of the Niger Delta. 8. It was observed that XP-07 washes clean from fingers and skin with any soap and tap water, quite unlike other pseudo-oil-based mud systems. This implies that XP-07 is in fact environmentally very friendly.

Application of direct hydrocarbon indicators for exploration in a Permian-Triassic play, offshore the Netherlands

This paper describes a case history of exploration in a Permian/Triassic play offshore the Netherlands. The seismic data in the area display clear direct hydrocarbon indicators. The purpose of this paper is to demonstrate how direct hydrocarbon indicators were used for the evaluation of undrilled prospects, in an attempt to determine hydrocarbon presence and hydrocarbon type. Prospect evaluation started with systematic screening of each prospect for acoustically soft amplitude anomalies and flat reflectors. Validation of hydrocarbon presence in these prospects was then attempted through the use of spatial filtering techniques for enhancing flat reflectors, and the use of a rock physics model, derived from well data, for the explaining observations. The type of hydrocarbons expected in each prospect was predicted using a comparison of forward modelling results and actual seismic observations. As a result of this approach, exploration drilling success has improved. Three recently drilled exploration wells all discovered hydrocarbons in previously validated prospects. We think that successful detection of hydrocarbons from seismic data is possible in this area due to favourable rock and fluid properties, reservoir thickness generally being greater than hydrocarbon column height, and the modest depth at which the reservoirs occur.

Case Study: Geomechanics Enables Successful Horizontal-Well Drilling in Libya

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 111384, "Geomechanics Enables the Success of Horizontal-Well Drilling in Libya: A Case Study," by Kaibin Qiu, SPE, Schlumberger; Julio Gonzalez Felgueroso, Gabino Lalinde, Abdulmagid Naas, and Bernard Coste, Akakus Oil Operations; and John Fuller, SPE, Schlumberger, prepared for the 2008 IADC/SPE Drilling Conference, Orlando, Florida, 4-6 March. The paper has not been peer reviewed. Highly deviated or horizontal wells can incur instability problems. A case in Libya is presented in which significant difficulties were encountered during drilling of the first horizontal development well in a field in the Murzuq basin. The first two branches of the well were lost to severe instability problems. A comprehensive geomechanics study was carried out to determine the causes of the wellbore failure and to improve drilling design and drilling performance of additional development wells in the field. Introduction Horizontal wells can increase production rates and ultimate recovery and reduce the number of platforms or wells required to develop a reservoir. The geometry also helps to delay water or gas breakthrough, bypass environmentally sensitive areas, and reduce stimulation costs. In 2006, Akakus Oil Operations began drilling of the first horizontal development well, Well H1, in a field in Libya to avoid water coning and delay water breakthrough. However, unexpected drilling difficulties were encountered, and the first two branches of the well were lost. Before this project, many vertical exploration and development wells had been drilled in the same block without experiencing any major problem. A wellbore-stability study was carried out to determine the cause of wellbore failure in the horizontal well. A mechanical Earth model (MEM) was built for the analysis. The analysis identified the cause of wellbore instability as inadequate mud weight while drilling the overlying shale formation in the deviation-buildup section. The design of the second horizontal well was optimized on the basis of this study, and it was drilled without problems and ahead of drilling schedule. This case demonstrated that a comprehensive geomechanics analysis could improve drilling performance and reduce drilling costs. Data Audit Erroneous or inadequate input data impair wellbore-stability-analysis results, even in the most advanced analysis model. Therefore, a data audit is the critical first step. Relevant data for a geomechanical study were selected and gathered. Data included extensive information from different domains, such as daily drilling reports, master logs, wireline logs, geological data and reports, petrophysical interpretations, seismic data, and general field information. Those data were analyzed and cataloged, and data availability was identified. Redundancy of data and use of data from different sources and domains were highly desirable to achieve an internally consistent description of rock properties and stresses. Cross-checking and comparing data from alternative sources can highlight errors, inconsistencies, and omissions in the data that may need to be fixed or filled in at a later stage to improve the robustness of the predictions.

Results of Extensive RSS Testing With PDC Bits

Technology Update Rotary steerable systems (RSSs) have made remarkable improvements in reliability since their introduction in the 1990s and have become a standard drilling tool. Today, point-the-bit and push-the-bit RSSs are used on both directional and vertical wells worldwide. No longer limited to high-cost offshore markets, their use is becoming more common in lower-cost land markets. In the following analysis, the results of an extensive series of test wells are described. The wells were drilled in a controlled, noncommercial environment, allowing single-step changes in the drill bit features and rotary steerable (RS) configurations. The testing was unique in that the specific RSS worked in shop-configurable point-the-bit and push-the-bit modes. Between the two distinct RSS operation modes, consistency in stiffness, weight, force-applying capability, and control systems led to a direct comparison of bit performance. The advancement of RS technology goes hand in hand with the use of polycrystalline-diamond-compact (PDC) bits. Continual development of advanced modeling software and cutters with significantly increased abrasion resistance have led to PDC designs that can drill faster, further, and with a high degree of stability. These benefits, combined with the appropriate RSS, can also deliver superior directional control, improved borehole quality, higher-quality logging, and easier casing runs. The resultant improvement in economics is particularly attractive in high-cost offshore wells. The bit-design optimization is key to the success of RS drilling. In directional applications, stability and steerability of the drill bit are critical to performance. Without a smooth torque response or a laterally stable design, drilling will not achieve the desired rate of penetration (ROP) or the durability necessary to drill the required interval. It is also important to match the side-cutting capability of the cutting structure and the gauge geometry to the operating mechanism of the specific tool and the directional objectives. These factors will affect the borehole quality, which has a direct impact on the directional control of the RSS. Maintaining wellbore quality, particularly borehole gauge, is crucial to both push- and point-the-bit systems for obtaining predictable directional response. Also, with any RSS, the directional control and borehole quality is directly linked as to how fast and precise the internal control system can operate. Rotary Steerable Bits There are four fundamental characteristics of the fixed-cutter bit: durability, steerability, stability, and aggressivity. Drill-bit designs need to be tuned with respect to bit profile, cutting structure, and gauge design to optimize performance for a given bottomhole assembly (BHA), formation, interval, mud type, and directional requirement. As with most RSSs, gauge hole and good borehole quality are very important in enabling the system to deliver consistent directional response. The lateral stability of the drill bit will play a direct part in this, particularly the cutting structure. Optimal RSS performance is obtained with drill bits that are laterally stable and drill with smooth response in terms of torque and rotation speed. Erratic torque and rotation-speed fluctuations will lead to problems with tool operation, inconsistent steering response, and ultimately to bit and tool failure.

Field-Development Case Study: Production Optimization Through Continuous Multidisciplinary Reservoir and Production Monitoring

Summary This paper presents a field-development case study of a low-permeability turbidite reservoir in Russia. The giant Priobskoye field contains 30°API crude in laminated sandstones of 0.1 to 20 md at a depth of approximately 2,500 m. The complex geology, lack of reservoir information and lack of technology availability caused a 20-year gap between discovery and development. The initial pilot development was halted after poor drilling success, thus the operator invested in 3D-seismic acquisition and an integrated, multidisciplinary reservoir modeling and simulation effort. The subsequent development was based on oriented water-flooding patterns and massive hydraulic fracturing, together with an artificial-lift system equipped with permanent pressure and rate monitoring for evaluation and real-time production enhancement. The optimization of operational practices and introduction of fit-for-purpose technologies enabled a production increase from an intermittent hundreds of BOPD to more than 75,000 BOPD in a period of 3.5 years. The exploitation strategy of this pilot area demonstrated commercially sustainable production from the reservoir and will form the basis for full field development.

EXPLORATION HIGHLIGHTS FOR 2006

Key business indicators show an upward trend in exploration activity in Australia during 2006. The year was marked by fluctuating high oil prices, a strong uptake of acreage in most basins, and increased levels of drilling activity and seismic acquisition. Market demand for product, production infrastructure and the fruition of several development projects have pushed the level of exploration activity in both offshore and onshore basins. Despite this trend and the spread of tenements, almost all petroleum discoveries made during 2006 were located within 15 km of existing (but often undeveloped) fields.The Carnarvon Basin continued to be the focus of most offshore exploration activity during 2006, with the highest levels of 3D seismic acquisition and exploration/appraisal/development drilling in the country. Discoveries in the Carnarvon Basin also covered the broadest range of water depths—extending from the oil and gas discoveries made by Apache on the inboard margin of the Barrow Subbasin, to the deepwater gas discoveries at Clio–1 and Chandon–1 by Chevron. Several large gas discoveries were made in the Carnarvon and Bonaparte basins and provide significant tie-back opportunities to existing and planned infrastructure. The Bonaparte Basin also saw significantly increased levels of 2D and 3D seismic acquisition during 2006. Onshore, the Cooper/Eromanga basins continued to experience the highest level of drilling activity and seismic acquisition, while maintaining an overall high drilling success rate. For the first time in many years, data acquisition also occurred in frontier basins like the Daly (Northern Territory), Darling (New South Wales), Tasmanian (Tasmania) and Faust/Capel basins (Lord Howe Rise region).Coal seam methane (CSM) exploration maintained a strong performance in 2006, particularly in Queensland, while South Australia, Queensland and Victoria continue to lead the way with large tracts of acreage gazetted for geothermal energy exploration.

An integrated approach with DighemV to groundwater exploration – Tsabong, Botswana

Exploration for potable groundwater to supply settlements in the southern Kalahari Desert of southwestern Botswana is currently in progress. A DighemV survey was flown over outcrops of Precambrian rocks after target areas were selected in an initial desktop study. The study included some preliminary ground geophysics, reviewed all available information in the area and completed an interpretation of remotely sensed (Landsat TM and SPOT) and aeromagnetic data. Two target areas were recommended for DighemV airborne electromagnetic (AEM) surveying near outcropping basement. The DighemV survey was designed to map faults and fractures intersecting resistive quartzite of the Olifantshoek Sequence, the most productive groundwater host in the area. Outcrop geological mapping, ground geophysical traverses to test previous successful boreholes and to locate new ones, exploration drilling and borehole logging were then used to follow up and refine targets generated from the AEM survey. Airborne and ground geophysical survey data were carefully integrated with outcrop geology and borehole information. An improved understanding of the geology and structure in Precambrian Olifantshoek quartzite was based on interpretation of the DighemV and aeromagnetic data. Exploration drilling success is attributed to an integrated multidisciplinary approach, which is strongly recommended for other potential groundwater projects in the Kalahari Desert.

EXPLORATION AND EXPLOITATION OF A MATURE BASIN SUCCESSFUL APPLICATION OF A PROCESS-DRIVEN MULTI-DISCIPLINARYTEAM APPROACH

From the early 1940s until the mid-1980s, hydrocarbon exploration within Austria was focussed upon Tertiary clastic reservoirs within the Vienna Basin. From 1980 to the early 1990s, an increasing number of exploration wells were drilled for carbonate reservoirs within deep thrust anticlines in the Alpine overthrust belt. These were typically high pressure-high temperature wells, and as a result, technically challenging and expensive.In the early 1990s, after little success within the Alpine overthrust belt, the focus of Austrian exploration was switched back to the 'maturely' explored Vienna Basin. During this period, the integration of historical well data, reprocessed 2D seismic and newly acquired 3D seismic data, evaluated within a sequence stratigraphic framework, has facilitated the accurate placement of multi-target wells. Together with the application of new drilling technology, the result has been a dramatic increase in new field discoveries. The reserves size of exploration and appraisal targets, in accordance with the maturity of the basin, have been relatively small, but, as a result of well-developed infrastructure and low drilling costs, highly profitable.The drive for increased drilling success and cost reduction and the application of 'new' technology has demanded an even closer integration of disciplines including exploration, reservoir engineering, drilling and production engineering. This integration in turn has necessitated process driven management. Multi- disciplinary teams, working with key contractors in an incentivised environment, achieved risk reduction, increased exploration success and budget reductions. As a result successful exploration has revived the mature Vienna Basin.

Cost Enectiveness of Well Site Selection Methods in a Fractured Aquifer

AbstractIn regions where ground water flow is restricted to sparse, narrow fractures, productive and nonproductive drilling sites frequently are separated by only a few tens of meters. Drilling success rates are low in these areas because favorable drilling sites occur infrequently and are difficult to identify. The drilling success rate can be increased when imagery and surface geophysics are incorporated into the site selection method. We present a method to evaluate the economic benefit of various site selection methods and show that the use of surface geophysics and aerial photography can reduce drilling costs by approximately a factor of two in an area with a low drilling success rate that is characterized by narrow fracture zones covered with several meters of weathered clays and thick vegetation. The benefits are smaller and less certain when social considerations are a strong factor in site selection.

AVO analysis in high‐impedance sandstone reservoirs

AVO analysis is now established as an effective hydrocarbon detection tool in many exploration provinces. In most areas in which it is widely used, the impedance of the reservoir rocks is less than or equal to the impedance of the surrounding rocks. The AVO response of low‐impedance reservoirs is an increase in amplitude with offset. Methodologies for detecting and analyzing these types of AVO anomalies have been developed, and have resulted in greatly increased drilling success ratios for some formations, such as the Yegua Formation of onshore Texas.

Deeper Geochemical Sampling Contributes to Texas Eastern Shelf Drilling Success: ABSTRACT

Deeper Geochemical Sampling Contributes to Texas Eastern Shelf Drilling Success: ABSTRACT

Stratigraphic Architecture of the Tonganoxie Paleovalley Fill (Lower Virgilian) in Northeastern Kansas

Lower Pennsylvanian paleovalley-confined sandstones are important petroleum reservoirs in the Midwest. In Kansas, such reservoirs have produced approximately 220 million bbl of oil and 1.7 tcf of gas. Valley-fill successions tend to become muddy upward, but there can be considerable local heterogeneity in which reservoir sandstones pass laterally into muddy sandstones or nonreservoir shales. The lack of understanding of this reservoir heterogeneity can lead to low drilling success rates. The Tonganoxie paleovalley (Upper Pennsylvanian, northeastern Kansas) contains facies very similar to Lower Pennsylvanian (Morrowan) valley fills, and can provide an outcrop- and subsurface-based model of sandstone deposition. The Tonganoxie paleovalley was incised during lowered sea level and filled during the subsequent transgression. The main paleovalley is approximately 41 m deep, 11 km wide, and 240 km long, and was fed by 1-km-wide tributary valleys oriented roughly normal to the trunk valley. Sandstones occur in four distinct architectural elements that were deposited during different phases of transgression. Type I sandstone consists of a belt of sandstone and conglomerate 3-18 m thick and confined to the trunk valley and wider portions of tributary valleys. Type I sandstone consists of amalgamated channel fills, has little or no mud, and has the highest porosity and permeability. The type I sandstone is overlain by estuarine deposits of sandstone (type II sandstones), rippled argillaceous sandstone to sandy mudstone, and coal. Most of the paleovalley was filled during this stage. The type II sandstones are narrow (1.5 km wide) arcuate bodies up to 8 km long and were likely deposited in tidal point bars near the fluvial to tidal transition, are either isolated sandstone bodies or are incised into type I sandstone. The higher mud content is expected to reduce porosity and permeability compared to fluvial facies. Type III sandstone bodies occur at the upstream limits of narrow tributaries and are probably bay-head deltas. Well logs indicate a range of mud content. Type IV sandstone is a thin (3 m) discontinuous sheet of marine sandstone deposited after most of the paleovalley had been filled.

Role of Sedimentological Modelling in the Success of Horizontal Drilling, C-7 Reservoir, Block I, Maracaibo Basin, Venezuela: ABSTRACT

Role of Sedimentological Modelling in the Success of Horizontal Drilling, C-7 Reservoir, Block I, Maracaibo Basin, Venezuela: ABSTRACT

Integrated petroleum project evaluation — three examples from the Denver-Julesburg Basin, Colorado

Abstract Integrating subsurface geology, seismic geophysics, and surface geochemistry enables more reliable evaluation of hydrocarbon exploration and production opportunities. We demonstrate the value of an integrated method by three case histories from the Denver-Julesburg Basin of Colorado, and present a simple technique for quantifying the geotechnical viability of projects. Drilling results validate the analytical methods applied and the technique used to integrate their findings regarding critical geologic parameters. With consistent application, the approach presented should improve the quality of project inventories and increase drilling success rates wherever it may be applied.

DEPLETION OF GAS RESERVOIRS BY MOLECULAR DIFFUSION — A CASE STUDY

Recent drilling in the southern Cooper-Eromanga basins of eastern central Australia has provided evidence to suggest that Permian gas reservoirs have been depleted by molecular diffusion.Diffusion is the process by which matter is transported along a concentration gradient, as a result of random molecular motion. It is a common and ubiquitous phenomenon in geological environments.In the Toolachee and Nappacoongee-Murteree blocks of PELs 5 and 6, channel sandstones of the Permian Patchawarra Formation are faulted or subcrop against the Murteree Horst basement high. The Lower-Middle Jurassic Hutton Sandstone was deposited directly over the exposed surface of this feature and the surrounding eroded Permo-Triassic topography. As a result, the truncated Patchawarra Formation sandstone reservoirs are in contact with the overlying Hutton Sandstone, a major fresh water aquifer within the Great Artesian Basin. There is an anomalous increase in Patchawarra Formation water resisitivity around the Murteree Horst, suggesting that fluid communication with the Hutton Sandstone has allowed ionic diffusion to reduce the salinity of the Patchawarra reservoirs.Fluid communication has existed between the Patchawarra and Hutton reservoir systems for the duration of hydrocarbon generation and migration. It is proposed that the diffusion of solution gas towards the Murteree Horst has lowered basinward Patchawarra gas concentrations below saturation point, to the extent that gas generated in nearby source areas has gone into solution rather than migrating in the gaseous phase to form accumulations. Hydrocarbon traps immediately basinward of the Patchawarra edge should contain gas only if the rate of supply from source rocks has been greater than the rate of loss by diffusion. Gas accumulations may be shielded from depletion by source areas or other accumulations which are closer to the Patchawarra edge.The diffusion model has a negative impact on the prospectivity of Permian gas targets in marginal source areas of the Cooper Basin where reservoir communication exists between potential gas reservoirs and the Great Artesian Basin aquifers. Nevertheless, the recognition of this process may be used to advantage in identifying areas where further gas exploration should be curtailed. Such action may improve the drilling success rate in the region.