Sufficient Conditions for Graphs to Be k-Connected, Maximally Connected, and Super-Connected

Let G be a connected graph with minimum degree δG and vertex-connectivity κG. The graph G is k-connected if κG≥k, maximally connected if κG=δG, and super-connected if every minimum vertex-cut isolates a vertex of minimum degree. In this paper, we present sufficient conditions for a graph with given minimum degree to be k-connected, maximally connected, or super-connected in terms of the number of edges, the spectral radius of the graph, and its complement, respectively. Analogous results for triangle-free graphs with given minimum degree to be k-connected, maximally connected, or super-connected are also presented

Strategies for the development of CBM gas industry in China

Since the environment for the CBM development in China has been changing in recent years, it is necessary to re-consider the relevant strategies. Through investigations, surveys, geologic assessment, strategic decision-making and other techniques, the strategies for CBM development in China were discussed in respect to present situations, opportunities, challenges, proved reserves, producing reserves, strategic principles, strategic countermeasures, time-spatial allocation of strategies, risk assessments, and elimination of relevant risks. Some research results were obtained. Firstly, still in its initial development stage with fast growth, the CBM industry in China has made outstanding achievements in six aspects and also faces challenges in six aspects. Secondly, strategic focus can be summarized as constructing six CBM production bases in Qinshui, Eastern margin of Ordos Basin, Southwest China, Changqing, Northwest China, and Northeast China, respectively, according to the principles of “steadily developing middle-high rank coals, accelerating the development of low-rank coals and strengthening the comprehensive utilization of mining gas wells”. It is expected that the producing reserves and peak-production rate will be 3–4 trillion m3 and 35–45 billion m3/a, respectively. Thirdly, major strategic risks in CBM development in China include low productivities of individual wells, improper understandings of geologic conditions, decline in investments and lack of technical reserves. To eliminate these risks, it is necessary to reinforce work in the following five aspects, namely, strengthening comprehensive exploration and development of coal-bearing formations, creating favorable environments for the development of private oil companies, expanding spaces for the growth of technical service companies, conducting more researches for the development of innovative technologies in more areas and intensifying law enforcement

Enrichment mechanism and exploration and development technologies of high coal rank coalbed methane in south Qinshui Basin, Shanxi Province

Based on analysis of the basic geologic characteristics and enrichment controlling factors of the high coal rank coalbed methane (CBM) in south Qinshui Basin in China, its enrichment mode, and exploration and development technologies are studied. Practices on the CBM exploration and development proved that the CBM reservoirs in this study area have the following three major properties: (1) High coal rank, strong adsorption ability, and good resources condition; (2) Low porosity, bimodal porosity structure, and obvious “bottleneck” of flow condition; (3) low reservoir pressure gradient that can constrain production. Based on deep analysis of high coal rank coal properties, this study proposes a coexistence and complementarity concept of structure, sedimentary, thermal power and hydro-geological conditions, and establishes a CBM dissipation model, which can simplify CBM enrichment problem and directly guide the region selection of CBM development. Five major critical technical systems have been formed for the CBM exploration and development in south Qinshui Basin: (1) Comprehensive geophyisical exploration and evaluation technologies; (2) Well drilling and completion technologies for high coal rank coal reservoirs; (3) Major reservoir treatment technologies; (4) Intelligent drainage and production control technologies; (5) Digital technology of coalbed methane field. These have effectively provided technical support for an orderly productivity construction of new CBM blocks. Key words: Qinshui Basin, high coal rank coal, coalbed methane, enrichment characteristics, enrichment condition, exploration and development technologie