Both the Rawlins and Schellhardt and Houpeurt analysis techniques are presented in terms of pseudopressures. Flow-after-flow tests, sometimes called gas backpressure or four-point tests, are conducted by producing the well at a series of different stabilized flow rates and measuring the stabilized BHFP at the sandface. Each different flow rate is established in succession either with or without a very short intermediate shut-in period. Conventional flow-after-flow tests often are conducted with a sequence of increasing flow rates; however, if stabilized flow rates are attained, the rate sequence does not affect the test. Fig 1 illustrates a flow-after-flow test.

This article discusses the implementation and analysis of the modified isochroncal testing for gas well deliverability tests. Both the Rawlins and Schellhardt and Houpeurt analysis techniques are presented in terms of pseudopressures. The time to build up to the average reservoir pressure before flowing for a certain period of time still may be impractical, even after short flow periods. Consequently, a modification of the isochronal test was developed[1] to shorten test times further. The objective of the modified isochronal test is to obtain the same data as in an isochronal test without using the sometimes lengthy shut-in periods required to reach the average reservoir pressure in the drainage area of the well.

The isochronal test[1] is a series of single-point tests developed to estimate stabilized deliverability characteristics without actually flowing the well for the time required to achieve stabilized conditions at each different rate. Both the Rawlins and Schellhardt and Houpeurt analysis techniques are presented in terms of pseudopressures. The isochronal test is conducted by alternately producing the well then shutting it in and allowing it to build to the average reservoir pressure before the beginning of the next production period. Pressures are measured at several time increments during each flow period. The times at which the pressures are measured should be the same relative to the beginning of each flow period.

Abstract Scale inhibitor (SI) analysis is an extremely important part of scale management and, in recent years, much work has been done on the development of specialist scale inhibitor analysis techniques like Liquid Chromatography Mass Spectroscopy (LCMS) to push the boundaries of low level scale inhibitor detection. However, LCMS requires costly and complex instrumentation and there was therefore still a need for the development of other advanced techniques like fluorescence (F) and Time resolved Fluorescence (TRF) that can be used on site to provide near "on line" data. Fluorescence techniques are particularly suited to tagged polymers and naturally fluorescent molecules like polyamines whereas the operation principle of TRF is based on interactions between lanthanide ions and various functional groups of polymer or phosphonate scale inhibitors. Both techniques work individually or in combination and this provides a distinct advantage for multiple scale inhibitor analysis in produced brines that enable the design of packages of different products for specific field applications. In addition, TRF and fluorescence techniques offer the capability of on-site detection compared to the majority of scale inhibitor analysis techniques and other advanced methods like LC-MS. The ability to detect both phosphonate and polymeric scale inhibitors at very low MIC (<1ppm) has the potential for significantly extending scale squeeze lifetimes. This has now also allowed highly efficient, F tagged polymers, to be used in field situations where scale squeezing was either stopped or the lifetime was significantly compromised because of the lack of confidence in the residuals analysis. Specific field and theoretical examples from both sub-sea and conventional wells will be presented where the application of both advanced fluorescence and TRF techniques has shown significant improvements in scale management. This paper will compare and contrast the pros, cons and limitations of both fluorescence and TRF techniques for both phosphonate and polymeric scale inhibitors. In addition, it will highlight examples where scale management significantly improves through the application of Fluorescence and/or TRF scale inhibitor analysis techniques in complex production scenarios.

Abstract For more than a decade, optimal value testing (OVT) has been advocated as a methodology that, in most cases, can replace conventional drillstem testing (DST) for in-situ permeability measurement. The term OVT refers to any pressure-transient test during which live hydrocarbons do not have to be produced directly to the surface (Elshahawi et al. 2008, 2012). Three primary types of well tests have been considered as part of the OVT toolbox: injection testing, wireline formation testing, and closed-chamber system testing with cleanup and repeat surges, which is a proprietary analysis technique. This paper reviews the earliest OVT case studies retrospectively, with the benefit of several years of production. These cases include the first successful multicycle well testing/fluid-sampling closed system testing operation with near-emission-free and real-time data transmission to surface in deep water. Operations were conducted from a moored vessel without the use of a subsea test tree, setting a world record at the time for the maximum depth at which any vessel had been moored. The operation successfully gathered all crucial data; the overall test duration was shortened; and most importantly, safety and formation fluid handling were enhanced with no hydrocarbons offloaded or flared. Data collected during all phases of the testing process were analyzed. These included the perforation, subsequent surge into the testing chamber, initial cleanup of flow/buildup, optimized closed-chamber surge flow, and final cleanup of flow/buildup. Standard techniques were used to analyze the traditional DST, but specialized techniques and software were developed to help plan and analyze the closed-chamber surge testing during perforation and surge testing. Data from the testing phase were used to generate an earth model to forecast production from the field. Several years of observed production confirm the early testing results and validate the OVT philosophy and the closed-chamber testing technology. This paper discusses the testing protocols, optimized system design, and novel analytical techniques employed. It also compares pressure transient analysis (PTA) results obtained from surge testing, standard DST, and formation tester. The consistency of formation pressure and permeability measurements obtained from the various testing techniques and the agreement with actual production performance lends credibility to the results and confirms their viability for replacing conventional DSTs in many cases. Particularly in deep water, where cost and environmental constraints limit the feasibility of conventional DSTs and where early data gathering is essential, such techniques can provide a powerful complement—and often a viable replacement—to well tests.

ABSTRACT

As the Oil and Gas industry expands its reach and moves into deeper water, the selection of the riser system is becoming more and more important from both a fatigue and strength perspective. The appropriate selection of riser system can make or break the concept evaluation for deepwater developments. For deepwater (>1500m) to date the industry has made use of SCRs, TTRs and SLORs. More recently we have seen Steel Lazy Wave Risers (SLWR) being considered. The advantage being they decouple the response of the riser from the vessel. However, in these deepwater applications Heave Induced VIV and VIV are becoming much more important and it is essential that the fatigue loading associated with these responses is captured adequately. This paper compares two different approaches for prediction of HVIV in a typical SLWR configuration. The two approaches include time domain wake oscillation assessment and an empirical VIV assessment. The analysis has taken into account the results of publicly available model test data on SLWR, as well as insights gained from other model testing programs. This paper will also address appropriate VIV analysis methodology for SLWR and considers the influence of Distributed Buoyancy Module particulars on VIV fatigue damage.

INTRODUCTION

HVIV

In an ideal case, HVIV is the occurrence of vortex-induced vibration caused by global motion of the riser through still water, rather than ideal VIV, which is a still riser in moving current.

HVIV, termed heave-induced VIV is generally a result of heave motions of a floating system, but HVIV type phenomena could also result from pitch/roll or surge/sway type motions depending on the attachment location to the floater. HVIV has also been observed on a mooring line (Carra et al., 2017). For SLWRs, HVIV is a concern primarily from a fatigue damage perspective. SLWRs are generally more susceptible to fatigue than SCRs because:

• There are no accepted VIV suppression solutions that can be fitted to the distributed buoyancy region
• The tension in an SLWR is lower than an SCR resulting in higher mode numbers being excited with corresponding greater fatigue damage rates.

The accurate and precise analysis of scale inhibitors--in conjunction with other field data such as ion analysis, total suspended solids, and productivity index--plays an important role in making decisions about the efficiency of scale squeeze and continuous chemical injection treatments. This paper presents a review of scale-inhibitor analysis techniques and describes how these techniques can be used to provide cost-effective scale management in simple and complex production scenarios. This overview of scale-inhibitor detection methods is based on a database of analytical techniques previously developed through a joint industry project and expanded to cover alternative approaches and recent developments in high-performance liquid chromatography, recently developed C18 ion pair approaches, improved benchtop polymer analysis for sulfonated polymers, and more recent methods such as time-resolved fluorescence (TRF) and other fluorescence-based approaches. The premise of this paper is that, although various methods are available for scale-inhibitor analysis, most are affected by interference of some degree and that, while a preferred method may be sensitive and accurate under a particular set of conditions, it is unlikely to be effective in all production environments. The scale-inhibitor analyst, therefore, requires a large toolbox of alternative approaches that can supplement original methodologies.

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 179900, “The Importance of Scale-Inhibitor Analysis in Scale Management—A State-of-the-Art Overview To Provide Cost-Effective Scale Control From Simple to Complex Production Scenarios,” by Stephen Heath, SPE, Baker Hughes; Gill Ross, Shell; and Gordon Graham, SPE, and Kirsty MacKinnon, Scaled Solutions, prepared for the 2016 SPE International Oilfield Scale Conference and Exhibition, Aberdeen, 11–12 May. The paper has not been peer reviewed.

The accurate and precise analysis of scale inhibitors plays an important role in making key decisions on the efficiency of scale-squeeze and continuous-chemical-injection treatments. Numerous techniques exist for scale-inhibitor analysis, ranging from the simpler methods to more-complex techniques such as high-pressure liquid chromatography (HPLC) and mass spectroscopy (MS). This paper presents a state-of-the-art review of scale-inhibitor-analysis techniques and describes how these techniques can be used to provide cost-effective scale management.

Introduction

Inorganic-scale deposition is a major problem encountered during production of oil and gas and is often managed by the use of chemical scale inhibitors to prevent scale from forming in the system through continuous chemical injection or by periodic batch squeeze treatments. In most cases, scale prevention through chemical inhibition is the preferred method of maintaining well productivity. Scale-inhibitor squeeze treatments provide one of the more common and efficient methods for preventing the formation of carbonate and sulfate scales in the near- wellbore region, tubing, and topside facilities of production wells.

The accurate and precise analysis of scale inhibitors plays an important role in making key decisions on the efficiency of scale-squeeze and continuous-chemical-injection treatments. Numerous techniques exist for scale-inhibitor analysis, ranging from the simpler methods to more-complex techniques such as high-pressure liquid chromatography (HPLC) and mass spectroscopy (MS). This paper presents a state-of-the-art review of scale-inhibitor-analysis techniques and describes how these techniques can be used to provide cost-effective scale management. Inorganic-scale deposition is a major problem encountered during production of oil and gas and is often managed by the use of chemical scale inhibitors to prevent scale from forming in the system through continuous chemical injection or by periodic batch squeeze treatments. In most cases, scale prevention through chemical inhibition is the preferred method of maintaining well productivity.

Abstract The accurate and precise analysis of scale inhibitors can play an important role in conjunction with other field data like ion analysis, total suspended solids and productivity index in making key decisions on the efficiency of scale squeeze and continuous chemical injection treatments. It is essential to have reliable data on scale inhibitor residuals in produced fluids to prevent wells from scaling and to enable maximum lifetime for scale squeeze treatments especially in complex operating environments. A variety of techniques exist for scale inhibitor analysis including the more simple methods like hyamine, fluorescence and Inductively Coupled Plasma Optical Emission Spectroscopy (ICPOES) to more complex techniques like high pressure liquid chromatography (HPLC) and mass spectroscopy (MS). All of these techniques, including combinations thereof, are currently in use and the advantages and disadvantages of each technique will be compared and contrasted for the different types of scale inhibitor. The impact of phosphorus speciation in phosphorus tagged polymers and for thermal degradation of phosphonates and phosphate esters will also be considered. Examples will be provided of how the analysis results can be misinterpreted if the wrong analysis techniques are used. In addition, specific scenarios in North Sea fields for treating conventional and co-mingled sub-sea wells will be discussed to highlight the use of scale inhibitor analysis techniques to aid chemical selection based upon chemical retention, minimum inhibitor concentration (MIC), detection limits and well production conditions. This paper will present a state of the art review of scale inhibitor analysis techniques and describe how these techniques can be used to provide cost effective scale management in simple to complex production scenarios.