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Based on the productivity equation of coalbed methane (CBM) well, considering the impact of coal reservoir reformability on gas well productivity, the main production layer optimization index in the “three-step method” of optimal combination of production layers is corrected, and then the CBM production layer potential index is introduced to evaluate favorable areas for commingled multi-coal seam production. Through analysis of the key parameters of coal reservoirs affecting the CBM productivity index, a development unit division method for areas with multi-coal seams is established, and a quantitative grading index system is proposed. On this basis, the evaluation process of CBM development favorable area is developed: the mature 3-D modeling technology is used to characterize the reservoir physical properties of multi-coal seams in full-scale; the production layer potential index of each grid is calculated, and the production layer potential index contour under single-layer or commingled multi-layer production are plotted; according to the distribution of the contour of production layer potential index, the quantitative index of CBM development unit is adopted to outline the grade I, II, III coal reservoir distribution areas, and thus to pick out the favorable development areas. The practical application in the Yuwang block of Laochang in Yunnan proved that the favorable area evaluation process proposed can effectively overcome the defects of selecting favorable development areas only relying on evaluation results of a major coal seam pay, and enhance the accuracy of the evaluation results, meeting the requirements of selecting favorable areas for multi-coal seam commingled CBM production. Key words: coalbed methane, reservoir physical property, joint mining, production layer potential index, development unit division, quantitative index, favorable area evaluation

The Dainan formation reservoirs in Shaobo area, Gaoyou sag, Southern China, sedimented mass conglomerates dominated by lacustrine slope apron system which fended by multiple flood channels with massive terrigenous clasts. In the early days, offshore fan-shaped sediments in the Shaobo area of the Gaoyou Sag were considered to be the main sedimentary system. However, a new lacustrine sedimentary model is presented in this paper. By careful core description and interpretation, four facies unions are recognized: (1) Facies union 1: Downslope clastic pathways that composed of massive conglomerates up to 6-25m thick, alternating with brown-dark gray mudstone and the etching structures can be often observed; (2) Facies union 2: Debris-flow Lobe is composed of massive conglomarates, matrix-supported to clast-supported polymictic conglomerates up to 10-50m thick; (3) Facies union 3: Underwater distributary channel is composed of trough cross-stratified sandstone, horizontally stratified sandstone and ripple cross-stratified fine to medium-grained sandstone, up to 5-20m thick; (4) Facies union 4: mudstone is dominates by thick grey black mudstone interbeding thin sandstone, the etching features are rare and bedding is typically parallel. In our study area, the traction current deposits constitute the producing petroleum reservoirs, and the conglomerates deposits are poor reservoirs. The sedimentary model may be applicable to other fault depression for predicting reservoir distribution.

The Chang 6 reservoir in Hulangmao area is a lithologic reservoir controlled by Zhidan Jingbian delta depositional system in Northern Shanxi Province. The oil reservoir has entered the middle-high-water-cut stage. The reservoir is characterized by low porosity and low permeability, with strong heterogeneity and great development difficulty. Therefore, it is necessary to further study the distribution of remaining oil through fine single sand body division and correlation，so as to improve the level of the reservoir development. Based on the theory of high-resolution sequence stratigraphy, according to the characteristics of mudstone marker bed and logging combinations, the sedimentary cycles are studied by using the techniques of maximum entropy spectrum and wavelet transform, and the cycle characteristics of different levels are clarified. Chang 6 member is divided into 3 fourth-level cycles, 6 fifth-level cycles (small levels), 13 sixth-order cycles (single level), and 21 seventh-order cycles (single sand body). Based on the stratigraphic correlation analysis model of sand body equal thickness, channel down-cutting, lateral phase transformation and splitting of superimposed sand body, and combined with the core and logging characteristics of the target area, the correlation framework of single sand layer in the whole area is established.

With the ability to provide complete profiles of pseudocolor image formation, IL (imaging logging) measures directionally, thereby offering a possible alternative to drilling and coring. This paper, relying mainly on IL information but also referring to formation dip angle logging information, details sandstone lamina dips and identifies sedimentary body dips, and sums up a practical palaeo-provenance direction judgment method using heavy mineral data analysis. By identifying a fine sandstone reservoir through an IL lithological model, a bedding model and a rhyme model, a 1D pseudoresistivity curve (named the 'IL rhythm curve') is, according to IL image analysis, extracted to assist in the interpretation of sedimentary microfacies and to establish an IL single-well facies analysis profile, overcoming an observance difficulty of IL in silty sandstone regions and intuitively displaying whole-horizon sedimentary evolution. As for a glutenite formation, calibrating IL information by rock cores, a single-well facies sequence of IL is established by identifying the Bouma sequence, high-density turbidity succession, the middle fan braided channel, the outer fan mudstone and other microfacies sequences, finely dividing the sedimentary facies sequence about sedimentary stage.