MODELING HYDRATES AND THE GAS HYDRATE MARKUP LANGUAGE

Natural gas hydrates, as an important potential fuels, flow assurance hazards, and possible factors initiating the submarine geo-hazard and global climate change, have attracted the interest of scientists all over the world. After two centuries of hydrate research, a great amount of scientific data on gas hydrates has been accumulated. Therefore the means to manage, share, and exchange these data have become an urgent task. At present, metadata (Markup Language) is recognized as one of the most efficient ways to facilitate data management, storage, integration, exchange, discovery and retrieval. Therefore the CODATA Gas Hydrate Data Task Group proposed and specified Gas Hydrate Markup Language (GHML) as an extensible conceptual metadata model to characterize the features of data on gas hydrate. This article introduces the details of modeling portion of GHML.


INTRODUCTION
The "Modeling" portion of GHML has assimilated information about gas hydrate modeling, consisting of such elements as name, purpose, main theories, and input/output parameters that are generally used in hydrate behavior modeling.The generation of this part of the GHML was essentially based on modeling software named "TOUGH-Fx/Hydrate," which is widely used for modeling gas hydrate resources."TOUGH-Fx/Hydrate" is a good representative of the state-of-the-art model in this research field.Therefore, although the GHML used a single software program as a reference, elements abstracted from it are likely to be suitable for most applications.
During the development of this part, we consulted many other international metadata standards (Markup Languages) that provided good references to structure design, naming conventions, annotation format, etc.
Consistency with these existing international standards ensures good communication and transferability between GHML and other international standard markup languages.

Naming convention
The naming convention in this standard is as follows: (1) Element The first letter of each concatenated word is capitalized, e.g.: InputParameter.
(2) Complex Type Each complex type ends with "Type," and the first letter of each concatenated word is capitalized, e.g.: InputType.

(3) Simple Type and Attribute
The first letter is lowercase, and the first letter of each subsequent concatenated word is capitalized, e.g.: valueList.

XML schema and namespace
This standard uses XML Schema to define the GHML.XML Schema is a recommended metalanguage by W3C that can define data element, data type, value space, and element relations conveniently and clearly.
"Namespaces in XML" lets browsers interpret more than one XML-based language in a single document without confusing different elements with the same tag names.This standard defines the following namespaces: targetNamespace = http://www.codata.org/ghml/xmlns:ghml=http://www.codata.org/ghml

DETAILS OF MODELING ML SCHEMA
The basic structure of this portion of GHML is shown in Figure 1.

Data elements:
• Input Parameter[ghml:InputType]: This is one of the most important elements in this portion, which includes five complex elements, each of which answers one important modeling question (as shown as     • RockGrainRadius[double] -The radius of the rock grain.

Figure 1 .
Figure 1.Basic Structure of Modeling Markup Language

Figure 12 .
Figure 12.SourcesSinkType Name[string] -Name for the well.Injection [ghml:InjectionType] -Defines production injection into a cell.Injection parameters will vary depending on the EOS being used (Figure13).In general, the user will specify a rate and an enthalpy for each component to be injected.The rates can be defined as constant (Rate [double] and Enthalpy [double]) or using a table to give time/rate pairs.

•
Cum_Rel_Mass[double] -Cumulative mass of released gas from the entire domain from the beginning of the simulation.• Cum_Rel_Volume[double] -Cumulative volume of released gas from the entire domain from the beginning of the simulation.• Free_Reservoir_Gas[double] -Volume of free gas in the reservoir at the time of observation.• Rem_Hydrate[double] -Mass of hydrate remaining in the deposit at the time of observation.ProductionPara[ghml:ProductionParaType] -Data describing gas production (rates and production stream composition at wells) • Time[string] -Simulation time.• Qm_CH4_prod[double] Mass rate of CH 4 production.Qv_CH4 _prod[double] -Volumetric rate of CH 4 production • CumM_CH4_ prod[double] -Cumulative mass of produced gas since the inception of the simulation.• CumV_CH4_ prod[double] -Cumulative volume of produced gas since the inception of the simulation.