7. INTANGIBLE ASSETS


	2017		2016		2015
Net book value Intangible assets		9,976		8,114		7,359
Provision for impairment of intangible assets		—		—		(80	)

		9,976		8,114		7,279

The evolution of the Group’s intangible assets for the years ended December 31, 2017, 2016 and 2015 is as follows:


	Service concession			Exploration rights			Other intangibles		Total
Cost		5,707			1,975			2,607		10,289
Accumulated amortization		3,475			150			2,271		5,896

Balance as of December 31, 2014		2,232			1,825			336		4,393

Cost
Increases		653			270			190		1,113
Translation effect		3,218			928			1,443		5,589
Decreases and reclassifications		(51	)		(183	)		20		(214	)
Accumulated amortization
Increases		180			—			143		323
Translation effect		1,904			5			1,296		3,205
Decreases and reclassifications		(6	)		—			—		(6	)
Cost		9,527			2,990			4,260		16,777
Accumulated amortization		5,553			155			3,710		9,418

Balance as of December 31, 2015		3,974			2,835			550		7,359

Cost
Increases		642			75			171		888
Translation effect		2,127			612			936		3,675
Decreases and reclassifications		(547	)		(584	)		127		(1,004	)
Accumulated amortization
Increases		437			—			280		717
Translation effect		1,245			—			848		2,093
Decreases and reclassifications		—			(6	)		—		(6	)
Cost		11,749			3,093			5,494		20,336
Accumulated amortization		7,235			149			4,838		12,222

Balance as of December 31, 2016		4,514			2,944			656		8,114

Cost
Increases		947			8			198		1,153
Translation effect		2,141			513			953		3,607
Decreases and reclassifications		(13	)		(149	)		185		23
Accumulated amortization
Increases		615			—			223		838
Translation effect		1,330			—			885		2,215
Decreases and reclassifications		—			(149	)		17		(132	)
Cost		14,824			3,465			6,830		25,119
Accumulated amortization		9,180						5,963		15,143

Balance as of December 31, 2017		5,644			3,465			867		9,976