Abstract

PVT phase diagrams are pivotal in predicting and guiding oil and gas production, especially in the volatile, condensate/wet gas (VCW) region, where the phase changes are very complicated. We compare the shale oil and gas systems both in Vaca Muerta (VM) formation in Argentina's Neuquén Basin and Shengli/Bohai (China) and show the similarities, and difference to VCW systems in the US. We present methods to characterize and optimize the production, including CO2 assisted recovery.

Introduction

The Vaca Muerta formation in Argentina's Neuquén Basin and Shengli field in China's Bohai Bay Basin have oil & gas fluids (VMSOG) have unique features that give them inherent advantages and disadvantages over the regular US high GOR Light Tight oil (HGLTO)counterparts.

For example, the VMSOG production has obviously slower GOR increase over time, but the production rates vary significantly. The causes from perspective of composition difference and phase diagram are discussed here.

There are also similar shale as well as conventional fluids as demonstrated in the Loma Campana block since the early development.

Then, the unique fluids’ PVT diagram properties of VM alike petroleum systems are compared with several major US and China shale and tight oil and gas fluids compositions. The potential for CO2 and natural gas IOR/EOR are discussed as well.

Theory and/or Methods

We use published open domain data from the following US LTO (Light Tight Oil) basins as well as VMSOG, i.e. Bakken, Eagle Ford, Permian and VM and Shengli oil fields. We also present internal data obtained from these fields, with detailed information unavailable in the public domain and discussed in details.

The oil and gas samples from VMSOG producing wells are collected and complete compositions are analyzed with high resolution Gas Chromatograph (GC), especially including the C1-C5 and light components as well. Saturated, Aromatic Resin and Asphaltene (SARA) are also conducted.

We attempt to use the difference in heavy (C7+, C15+ and C20+) and light components (C1 through C5) of the fluids to simulate the fluids’ PVT phase diagram. Then, common well-bore PVT conditions are used for simulation of the production.

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