Offshore oil and gas reservoirs comprise a significant portion of the world’s reserve base, and their development is expected to help close a potential gap in the supply of hydrocarbons in the near future. Continuous advances in technology have helped the oil and gas industry to extend the exploration and production activities to deep and ultra-deep waters in harsher environments. Field development in the offshore environment is associated with numerous significant challenges in different phases including exploration, reservoir description and characterization, development planning, drilling, production, improved oil recovery (IOR) and enhanced oil recovery (EOR), transportation, and decommissioning. These challenges are further complicated by economic restrictions, especially in periods when low or unstable oil prices weaken the incentives of investments due to the high risks and uncertainties involved. Environmental concerns including the adverse effects of seismic surveys, drilling activities, discharge of waste material and produced water, and accidental spills and blowouts add another level of complexity to the design and implementation of offshore projects. Safe, reliable, and efficient development of offshore hydrocarbon reservoirs can be achieved through the proper identification of the challenges and use of modern technologies and innovative methods. This work is an effort to provide a comprehensive review of the history, global distribution, production share, classification, characteristics, and characterization methods of offshore reservoirs, and some of the main aspects and challenges of the experimental and modeling works as well as IOR/EOR planning and implementations from the reservoir engineering and production standpoint. These challenges are categorized based on their area of impact, i.e., characterization and recovery (production) phases. Furthermore, economic and environmental challenges are reviewed. After the recent downturn that caused a decline in offshore investments, current investment trends and the forecasts show that the offshore industry is booming again with more focus on cost saving and operational efficiency. The key technologies that can expedite the growth of the offshore petroleum industry have also been discussed.

Technical and Non-technical Challenges of Development of Offshore Petroleum Reservoirs: Characterization and Production

Building Systematic Approach for Upscaling Flow Potential in South East Asia Deepwater


 The past few years have been challenging for the oil and gas industry. Many processes and operations have needed to adapt to lower oil and gas prices, caused in part by the COVID-19 pandemic. Understanding reservoir producibility and proving reserves are keys to generating a reservoir field development plan (FDP). However, the different processes to obtain such answers are strongly dependent on cost. The value of information is an extremely important criterion for operators to decide whether to proceed with their discoveries.
 In an interval pressure transient test (IPTT), a formation tester is used to pump a fluid from a single point or small interval of the formation into the wellbore. Zones of interest can be isolated and tested separately zone by zone. Mud filtrate and reservoir fluids are pumped continuously using the downhole pump, and a downhole fluid analyzer (DFA) is used to monitor the fluid cleanup process. The post-pumping p pressure buildup can be analyzed in a similar manner to traditional well test analysis. Such IPTT have been available since 1980s; however, comparisons of IPTT to actual well tests and other permeability measurements were rarely published until the early 2000s. IPTT have been widely used in the past 20 years, especially in combination with dual packers, and more recently with single packers. Operation efficiency and safety have improved significantly. However, interpretation of the pressure transient obtained from an IPTT is not always well understood.
 Frequently asked questions (FAQs) include the following: What is an IPTT or a vertical interference test (VIT)?How does an IPTT compare with other permeability measurements?What are the different scales of pressure transient data?How do we upscale zone permeability to an entire reservoir interval?What is next?
 This paper will address these questions using both reservoir simulation and field data. The field examples are from different environments, ranging from shallow marine to turbidite to deepwater environments, with different fluid systems, such as black oil, heavy oil, waxy oil, gas, and gas condensate. Geographically, the field data include examples from South East Asia and the Middle East. Permeability obtained from pretests, IPTT, nuclear magnetic resonance (NMR), core analyses, and well testing will be compared.
 Recently deep transient testing (DTT) has been introduced in the industry. With DTT, we can flow faster and longer than previously possible with formation testers, enabling pressure transient analysis in higher permeability and thicker formation. Further data quality improvements come from new, high-resolution gauges deployed with an intelligent wireline formation testing platform. This paper includes a review of the DTT method with several field examples.
 Finally, the advantages and disadvantages of the different testing methods are discussed relative to the test objectives, with the intent to provide a cost-effective data selection method to ensure sufficient FDP input and to justify the value of investment to the relevant stakeholder.

Frequently asked Questions in the Interval Pressure Transient Test (IPTT) and what is Next with Deep Transient Test (DTT)


 Mini-DST, as alternative to conventional DST, has been in the industry more than 30 years, and its economic value has showed the advantage over DST, however limited permeability-thickness and investigated radius is a bottle neck which in many cases has much uncertainty to support reservoir characterization. The recently developed Deep Transient Testing technology improved its performance over former mini-DST technology in terms of longer pumping time, larger produced volume, and greater investigation radius. This paper presents a study in a variety of environments and applications, demonstrating how formation testing is being planned, acquired, and used in new ways, including Deep Transient Testing (DTT). The comprehensive radial model approach based on DTT using integration of well logs, numerical simulation grid and pressure transient behavior is built for the first time.
 To design an effective approach to generate a radially gridded single well predictive model, this workflow requires knowledge of well performance, petrophysics and reservoir simulation. This simulation workflow started with a petrophysical interpretation together with well surveys which serve as essential input data to build a single well predictive model. Rock typing using Heterogenous Rock Analysis (HRA) method resulted in a more detailed properties population along the vertical direction in tartan grid. Defining completions of the well and followed by conversion of tartan grid to radial grid was performed to accurately capture the pressure transient response near wellbore. The radial grid model was setup as a DTT model to forecast the pressure transient behavior of the reservoir incorporating the technology of a new intelligent wireline formation testing platform in the simulation inputs.
 The outcome of this study produced multiple scenarios incorporating different reservoir tightness from low to high with known thickness. The reason is that as the formation gets tighter; it is more challenging to achieve radial flow and predict producibility. By having uncertainty study in place, we can understand the outcome of each scenario then provide quantitative data to make decision on DTT feasibility, inlet and flow manager selections based on simulation result. This methodology not only optimizes the operation planning and execution, but also estimates pressure drop and the time needed to be on stationary for operational risk mitigation, which are in place to help operators improve certainty in decision making.
 The case study showed that the advanced 3D radial grid predictive model method addressed the advantage of Interval Pressure Transient Testing (IPTT) and DTT in accessing and evaluating reservoir connectivity, heterogeneity, and drainage radius. In this paper, we are the pioneer in this robust Intelligent FT integrated workflow globally, which was successfully implemented together with all wireline operations within planned time frame involved and delivered with exceptional results.

Pioneer in Integrated Workflow for Deep Transient Testing (DTT) from Interpretation to Forecast

Abstract Reservoir characterization is a main objective in oil &amp; gas exploration where permeability-thickness, skin factor, reservoir boundaries, production potential and reservoir fluids are the key values. However, sustainability currently plays an important role which often translates to zero flaring compliance. Deep Transient Testing (DTT) is a new generation wireline formation testing technique investigating higher permeability and thicker reservoir packages with increased radius of investigation (ROI) compared to traditional Interval Pressure Transient Testing (IPTT) by flowing faster and longer and by using higher resolution pressure gauges. DTT is not a replacement for Drill Stem Testing (DST), but rather an approach to bridge the information gap between IPTT and DST, mainly used in green fields, especially in multi reservoirs where it is costly to test all potential zones. Offset well data are used to build a preliminary numerical model for feasibility study in the target well. As soon as recorded, relevant logs such as Nuclear Magnetic Resonance (NMR) and image logs are used to select pressure, sampling, and DTT points and to derive reservoir properties and facies description to update the numerical model. Innovative workflows, from thin beds sand count and resistivity to permeability anisotropy calculation, are employed. During the DTT acquisition, real time monitoring and constant communication between parties is critical for an effective operation. In-situ reservoir fluid data and pressure transient data are constantly analyzed and integrated into 2D and 3D space in an open and collaborative digital cloud environment. Additionally, a 3D geo-context is created using geological and petrophysical data, optionally combined to seismic information. The last step of the workflow consists of dynamically calibrating this static model to obtain insights such as well deliverability, reservoir connectivity or minimum hydrocarbons in place. Two case studies are presented to demonstrate the value of the workflow which is applied to a complex reservoir consisting of multi layers with cross flow production potential. The DTT objectives include determining the reservoir flow potential, de-risking the presence of baffles, and to estimate the volume of influence of the test. DTT analysis and history matching is used to address reservoir uncertainties for field development planning. In addition, the total DTT produced CO2 emission is compared to traditional testing methods and shows a 70-80% reduction in CO2e (CO2 equivalent) quantities. For Malaysia alone, a total of 2,130 metric tons of CO2 emissions were reduced, equivalent to 481 cars off the road annually with 3 DTT stations. This paper presents a complete digital workflow applied to several green fields in Asia-Pacific region that leads to successful DTT operations initiated from intelligent planning which positively impacted the field development decisions. 

Driving Deep Transient Testing with a Complete Digital Workflow – A Sustainable Exploration in Green Fields

Reducing the Appraisal Uncertainty with Advanced Wireline Formation Testing Technology: A Case Study from the Gulf of Thailand

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Building Systematic Approach for Upscaling Flow Potential in South East Asia Deepwater

Reducing the Appraisal Uncertainty with Advanced Wireline Formation Testing Technology: A Case Study from the Gulf of Thailand