Abstract Construction work above previous mining area is always a great challenge from the engineering point of view. In the southern part of Budapest, the previous mining activities resulted more than a hundred thousands of square meters of cavities. These cellars cut into porous limestone with different depth, but mostly close to the surface; nowadays, these cellars are located inside a residential area, and some part of the undermined area is planned to build because this is an empty and valuable area. For the construction of these improvements, it is necessary to perform detailed investigations and stability calculations.This paper is introducing the detailed investigation process of a significant cellar which will be involved by construction activities. Three buildings are planned to build above it. The studied cellar located in the 22nd district of Budapest, Hungary, with a depth between 4.3 – 7.7 m, with a wide range of pillars’ width between 0.73 – 7.7 m according to the studied cross-sections. The investigation starts with geometrical measurements and core drillings to map the rock mechanical properties of the host rock. Several laboratory tests were done for obtaining rock mechanical parameters for modelling. After creating the geotechnical model, it was used for FEM calculations using RS2 software. Four cross-sections were chosen across the cellar system in different locations and various directions modelling the surface load of the planned building. The stability of the cellar was studied from two different viewpoints: firstly, the factor of safety was determined, and secondly, the settlement was calculated as an effect of the surface load. A displacement measurement system was set up in several cross-sections of the cellar to compare the calculated and real displacements in the future. Introduction Geotechnical problems are one of the issues which solved nowadays with the help of numerical modelling. One of the serious problems in this field is the stability of underground cavities, both man-made and natural ones.

Brian Sullivan, SPE, joined IPIECA as executive director in 2011 following a 23-year career with BP. He graduated in metallurgy and materials science from Imperial College, London, and was recruited into BP’s Refining and Marketing international graduate program in 1986. Sullivan’s career with BP included assignments in London, Copenhagen, Budapest, Athens, and Johannesburg and business experience in more than 60 countries. During his time with BP, he has had a varied career of technical, commercial, financial, and leadership roles across the downstream value chain including crude and products trading, marine fuels, lubricants, and alternative energy.

Abstract A combined 400+ km of single- and multichannel seismic reflection data were acquired on Lake Neusiedl in northeast Austria in May 2013. This geophysical campaign was a multinational academic effort among the Universities of Vienna, Budapest, Bremen, and Southampton. Lake Neusiedl is an exceptionally shallow lake, with an average water depth of only approximately 1.4 m. Although high-resolution single-channel seismic reflection data have been collected before on this lake, the multichannel seismic acquisition, towing a 60 m cable and an air gun behind a retrofitted ferry boat, was a completely new approach in this area. The quality of the multichannel data turned out to be exceptionally good; i.e., the high-frequency data illuminated the subsurface of the lake for the first time, down to the pre-Cenozoic basement at approximately 600 m depth. The most prominent findings of the new data include (1) a consistent southeasterly dip of erosionally truncated Late Miocene (Pannonian) sediments beneath a very thin Holocene mud layer, (2) the presence of major throughgoing fault systems (including a positive flower structure), (3) at least one Pannonian progradational sequence defined by seismic clinoforms indicating a paleowater depth of approximately 40–80 m, (4) flat spots in several locations of the study area corresponding to possibly biogenic gas in a few hundred meters depth beneath the lake, (5) vertical data wipeouts, which are interpreted as gas chimneys reaching the lake bottom, and (6) definition of the pre-Cenozoic basement. Interestingly, the gas chimneys are interpreted to correspond to the well-known gas seeps (“Kochbrunnen”) in Lake Neusiedl, which were originally described as subaqueous water springs on the lake floor responsible for ice-free areas in the lake ice cover during winter.

Abstract MOL Group is an integrated, international oil and gas company headquartered in Budapest, Hungary, with lead position in its core markets within Central and Eastern Europe. Its northern region downstream business consists of two complex refineries and three steam crackers at two locations. To be able to exploit synergies thus to maximize potential profitability of assets via transfer connections, current downstream planning activities are performed on group level in a multi-site linear planning model resulting in simultaneous optimization possibility of petrochemical and refinery sites. In such a planning model system, next to internal asset constraints, specific utility costs and market purchase or sales conditions drive the optimization result. It does not only support optimal feedstock selection for both refinery (different crude oils provide different yield structure) and petrochemicals (LPG against naphtha feedstock) together with their most profitable asset configuration, but it also enables proper setting of refinery product portfolio against polimer production. In current MOL Group solution, an additional aspect has been implemented for improving the refinery-petrochemical connection: next to its volumetric effect, specific quality of produced petrochemical naphtha feedstock is also considered within the optimization as this information is channeled into the olefin plants in order to better estimate monomer yields of the steam cracker. It provided another milestone of this simultaneous optimization challenge thus improved on its delivered results. The paper focuses on our current best practices by demonstrating how above planning system features support MOL Group Downstream to derive right business decisions. It furthermore explains how our development roadmap puts emphasis on further refinement of the refinery-petrochemicals connection, utilizing state-of-the-art technologies like upgrading our linear optimization models with non-linear correlations.

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 174174, “Integrated Approach To Managing Formation Damage in Waterflooding,” by Sergey Aristov, Paul van den Hoek, and Eddie Pun, Shell, prepared for the 2015 SPE European Formation Damage Conference, Budapest, Hungary, 3–5 June. The paper has not been peer reviewed. Understanding of formation damage is a key theme in a waterflood project. An integrated multidisciplinary approach is required to determine an optimal design and strategy. An operator has developed a suite of tools to tackle these issues and help in adequate design and optimization of waterfloods. Introduction Many waterfloods in the operating phase do not perform as expected. Often this is because of well-injectivity issues where the required water quality for the injected water is either not properly defined (i.e., by the subsurface disciplines) or not properly managed (i.e., at the surface facilities). A rapid decline in well injectivity can result when injecting under matrix conditions, and a loss in reservoir containment caused by out-of-zone injection (OOZI) or a short-circuiting injector and producer can occur when injecting under fractured conditions, all negatively affecting reservoir sweep. Subsurface and Subsurface-Modeling Work Flows To determine an optimal waterflooding concept, it is important for the integrated work flow that the outcome of the sub-surface assessment be a range of technically feasible scenarios. These scenarios should incorporate the ranges in subsurface uncertainties combined with sub-surface concept options. The objective for the subsurface work flow is to define for each of these scenarios the production profile for the field, injection volume, quality of injected water, number of injection wells, subsurface targets, risk, and mitigations. The subsurface work flow is illustrated in Fig. 1 of the compete paper. The following main steps are identified: Identification of potential water sources. All available water sources need to be identified, and a screening should be performed by assessing the compatibility of the injected water with the clays in the reservoir (i.e., risk of clay swelling). Injection targets for field development. On the basis of the expected reservoir performance for waterflooding in a field development, the targets for the total water-injection volume for the (full) field should be defined.

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 174169, “Controlling Losses When Recompleting Low-Pressure Reservoirs,” by G. Uguna, Petroamazonas, and R. Rachid, SPE, A. Milne, SPE, and S. Ali, SPE, Schlumberger, prepared for the 2015 SPE European Formation Damage Conference, Budapest, Hungary, 3–5 June. The paper has not been peer reviewed. A challenge in many permeable, water-sensitive, subhydrostatic reservoirs is avoiding the loss of completion fluid when completing or working over wells. To overcome the limitation of conventional fluid-loss-control pills, a low-viscosity system was developed. The system is composed of a viscous disproportionate permeability modifier (VDPM) with sized synthetic polymer particles and fibers, which degrade into organic acids. The VDPM reduces the effective permeability to water-based fluids, and the sized particles create an impermeable filter cake. When the particles degrade, the organic acid acts to break any remaining polymer. Traditional Polymer-Gel Systems The limitations of many conventional fluid-loss-control pills have resulted in the development of a number of solids-free fluid-loss-control pills. In high- permeability reservoirs, a highly crosslinked gel is needed to achieve good fluid-loss control. Polysaccharides, such as guar, have been widely used for this application because of their low cost and availability. These guar-based fluids are typically crosslinked with borate or organometallic crosslinkers. The viscosity of crosslinked guar decreases significantly at temperatures greater than 200°F because of the limited thermal stability of the polymer. For higher-temperature applications, polyacrylamides can be used to form crosslinked gels. A limitation of crosslinked polysaccharide and polyacrylamide polymers is that they require an internal or external breaker. The breaker is required to break the crosslinked polymer and lower the viscosity of the fluid so the broken gel can flow out of the formation matrix. Even when using an internal breaker, some polymer remains in the pore spaces, effectively reducing and damaging the permeability of the formation. To overcome the limitation of residual-polymer damage, hydroxyethylcellulose (HEC) has been used extensively because of its low residual-solids content. However, linear HEC polymer solutions do not form rigid gels but control fluid loss through viscosity and gradual filtration. This means that, as the linear fluid penetrates deeper into the formation, the shear rate decreases and the apparent viscosity increases. Permeability damage has been shown to increase with increasing penetration of viscous fluids, not only with HEC. Despite all the advances made regarding the design of fluid-loss-control pills, the greatest challenge remains the same, which is to have a fluid that prevents the loss of water-based fluids into the reservoir but does not limit the production of crude out of the reservoir when the well is put on production.

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 174279, “Formation-Damage Diagnosis Facilitates a Successful Remedial- Treatment Design and Execution in Sandstone Horizontal Oil Producer: A Laboratory and Field Case Study,” by M.A. Bataweel, SPE, A.H. Al-Ghamdi, SPE, P.I. Osode, SPE, T.A. Almubarak, SPE, E.S. Azizi, SPE, Eddy Sarhan, SPE, and M.G. Al-Faifi, SPE, Saudi Aramco, prepared for the 2015 SPE European Formation Damage Conference, Budapest, Hungary, 3–5 June. The paper has not been peer reviewed. Well-control fluids were used during a routine overbalanced workover operation in an offshore well completed in high-permeability sandstone. A fluid-loss-control pill was used to control excessive losses; however, because of the high permeability of the reservoir and the absence of sized particles in the pumped pill, a large amount of fluid was lost to the formation. A comprehensive review, accompanied by laboratory work, was conducted to identify the damaging mechanism and formulate a remedial treatment. Introduction Polymer-based fluids are beneficial in terms of generating viscosity to clean out the wellbore during any well intervention. Improper polymer selection has led to significant formation damage in several situations. Polymers also can invade the high-permeability zones, hampering hydrocarbon flow through the zones. Bipolymers generally are removed through acidizing, which breaks down the polymer backbone. The damage caused by polymers can be minimized with proper polymer selection. Standard remedial treatments for removing the near-wellbore polymer include injecting solvents (e.g., xylene), acids, alcohols, glycols, surfactants, or a mixture of these liquids into the well. In sandstone well treatments, formation composition should be considered carefully, especially minerals susceptible to acid attack. Three potential damaging mechanisms can occur during sandstone acidizing: formation deconsolidation in acid; reprecipitating during primary, secondary, and tertiary reactions; or the release of fines because of partial decomposition of minerals in acid. In the case of damage with oil-based material or emulsions, microemulsion treatments have been recommended. The microemulsion will solubilize the oil and emulsions and fluidize the filter cake into a single mesophase while dissolving the acid-soluble particles and making the solids and formation rock water-wet. The oil-based-mud particles in a filter cake will disperse, allowing the produced fluid to displace these blocking particles from the damaged zone into the wellbore and through any screens.

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 174273, “Study of Filtrate and Mudcake Characterization in High Pressure/High Temperature: Implications for Formation-Damage Control,” by Saeed Salehi, SPE, University of Louisiana at Lafayette; Ali Ghalambor, SPE, Oil Center Research International; Fatemeh K. Saleh, University of Louisiana at Lafayette; Hadi Jabbari, SPE, University of North Dakota; and Stefanie Hussmann, University of Louisiana at Lafayette, prepared for the 2015 SPE European Formation Damage Conference, Budapest, Hungary, 3–5 June. The paper has not been peer reviewed. This paper focuses on experimental methods quantifying water-based muds and investigating effects on particle bridging, filtrate invasion, and permeability. To show the particle-bridging effect, high-pressure/high-temperature (HP/HT) filtration tests were conducted on sandstone cores with permeability ranging from 10 md to more than 1100 md. Analytical models were used to calculate mudcake permeability for the tests using different mix designs. The results from this study can be applied to designing wellbore-strengthening fluids to mitigate formation damage. Introduction In an overbalance situation, the fluid phase of the mud, called filtrate, invades the formation, whereas solid particles of the mud build up mudcake. Characteristics of filtrate and mudcake are strongly controlled by mud particle type, size, and concentration. It is often desirable for a mud to leave a thin, low- permeability cake that helps with near-wellbore stability and strengthens the wellbore. The goal is to reduce the amount of whole mud flowing into the formation and to prevent loss of circulation, which causes many drilling-related problems. Drilling-fluid particles present different sizes; the larger particles form the first layer of the filter cake, and the smaller particles deposit within the cake formed by the larger particles. At the same time, the filter cake is undergoing compaction by the effect of the fluid drag as the smaller drilling-fluid particles are flowing through the filter cake. As a result of the deposition and compaction undergone by the filter cake, the thickness of the cake and its porosity and permeability will vary, thus affecting the performance of the filtration. During filtration, new particles are deposited on the surface of the cake and, over time, the thickness of the cake increases until filtration subsides. Filtrate behavior of the drilling fluid affects the permeability of the filter cake. Thin mudcakes, which have low permeability, strengthen the wellbore; however, thick mudcakes can cause operational problems such as stuck pipe, excessive torque, drag, and high swab and surge pressures. Lost-circulation material, such as properly sized calcium carbonate, can prevent leaks of whole mud into the formation, which, in turn, prevents leaks of the base fluid such as oil or water. These two chain processes significantly increase wellbore strength to prevent fractures or fracture propagation.

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 174180, “Integrated Approach to Sand Management in Mature-Field Operations,” by M. Ruslan and P.Y. Lee, Dong Energy, prepared for the 2015 SPE European Formation Damage Conference, Budapest, Hungary, 3–5 June. The paper has not been peer reviewed. An integrated approach to sand management is crucial to address sanding risk in producers and injectors in a North Sea mature field. The concept incorporates the Lean Six Sigma approach and is developed with a major focus on the rehabilitation of mature fields, where each barrel of oil counts and uncertainty (both technical and economical) is an increasing challenge. High decline in productivity and increased operational challenges are common issues for mature fields. Introduction The Siri asset comprises a series of marginal mature fields. They are located 220 km from the coast parallel to the northwestern edge of the Danish sector of the North Sea, with average water depth of 60 m. The relatively weak cemented fine- to very-fine-grained Paleogene sandstones from the Siri Canyon in the Danish North Sea are characterized by high content of glauconite, occasionally greater than 30%. The high glauconite content is a result of the sand being stored at the sediment-starved Stavanger platform before being shed into the North Sea by density and mass flows. After deposition, controlled by seafloor topography and pre-existing gullies, the sands experience remobilization in various degrees. The reservoir quality is generally good, with high porosities and high permeability. The asset is currently under waterflooding secondary recovery, with the main objective being pressure support and displacement efficiency in respective parts of the reservoir. Multiple enhanced-oil-recovery projects are ongoing or under evaluation, such as simultaneous water and gas injection and huff ’n’ puff gas injection.

ABSTRACT Under certain circumstances, marine streamer data contain nongeometrical shear body wave arrivals that can be used for imaging. These shear waves are generated via an evanescent compressional wave in the water and convert to propagating shear waves at the water bottom. They are called “nongeometrical” because the evanescent part in the water does not satisfy Snell’s law for real angles, but only for complex angles. The propagating shear waves then undergo reflection and refraction in the subsurface, and arrive at the receivers via an evanescent compressional wave. The required circumstances are that sources and receivers are near the water bottom, irrespective of the total water depth, and that the shear-wave velocity of the water bottom is smaller than the P-wave velocity in the water, most often the normal situation. This claim has been tested during a seismic experiment in the river Danube, south of Budapest, Hungary. To show that the shear-related arrivals are body rather than surface waves, a borehole was drilled and used for multicomponent recordings. The streamer data indeed show evidence of shear waves propagating as body waves, and the borehole data confirm that these arrivals are refracted shear waves. To illustrate the effect, finite-difference modeling has been performed and it confirmed the presence of such shear waves. The streamer data were subsequently processed to obtain a shear-wave refraction section; this was obtained by removing the Scholte wave arrival, separating the wavefield into different refracted arrivals, stacking and depth-converting each refracted arrival before adding the different depth sections together. The obtained section can be compared directly with the standard P-wave reflection section. The comparison shows that this approach can deliver refracted-shear-wave sections from streamer data in an efficient manner, because neither the source nor receivers need to be situated on the water bottom.